Rookies:Suggested Reading
First things first! I want to give massive credit to Howesmath (please rep her for sharing her approach - see the post below (#2)). Her approach is more accurate than mine (I have shown a way to make mine somewhat accurate in the example by estimating the tax) but usually I am too lazy to do it her way

Here is my (somewhat) simplified approach:
1.) I start by totaling the value of all items. I write that number down
2.) The next step is to convert everything to a pre-tax basis. To calculate this, I add up all the manufacturer Q's and divide by the quantity 1+tax rate. In my case, Michigan has a 6% tax rate. Therefore, I divide the manufacturer Q total by 1.06. The resulting value is on a pre-tax basis.
3.) You then add up all your CVS Qs.
4.) You then take the item total and subtract both CVS Qs and the calculated manufacturer Q value (from step 2). Your ECBs need to be the largest value possible that does not exceed this.
5.) OOP = (the calculated value from step 4 - ECBs you have) * (1+ tax rate). i.e. $0.33 * 1.06 = $0.35
The only time this does not work perfectly is if your Manu Qs are for non-taxable items or you have Qs that require adjustment/cashier input. This can be partially fixed by handing the Qs in the following order.
1.) $$/$$, 2.) ECBs, 3.) CRTs, 4.)other CVS e-mail Qs 5.) Manufacturer Qs that require adjustment/cashier intervention 6.) Normal Manufacturer Qs
************************************************** **** HYPOTHETICAL EXAMPLE ************************************************** ****
Purchasing:
1 * $4.99 Tylenol RR
2 * $2.99 Pledge Dusters
2 * $1.49 Palmolive
5 * $1.00 Propel
1 * $14.99 Contour
2 * $3.29 Crest Pro Health Night TP
4 * $1.99 Lumene Body Aktiva (.34 oz)
1 * $2.49 CVS Beauty soap 3 pack
Total = 4.99 + 5.98 + 2.98 + 5.00 + 14.99 + 6.58 + 7.96 + 2.49 = $50.97
Coupons:
1 * $5.00 Tylenol - will require override to $4.99
2 * $3.00 Pledge Dusters - will require override to $2.99
2 * $0.40 Palmolive
5 * $0.50 Propel tearpad
1 * $14.99 Contour (assumes you have a written prescription for someone)
1 * $3.29 Crest Pro Health Night TP (Bogo Q)
Total = 4.99 + 5.98 + 0.8 + 2.50 + 14.99 + 3.29 = $32.55 / 1.06 = $30.71
1 * 2/10 CVS products CRT
1 * 2/10 CVS e-mail (different code than CRT)
1 * 10/50 crt (for the purposes of this example, we will pretend that there was a $10/50 e-mail available)
Total = 2.00 + 2.00 + 10 = $14
Total Qs = $44.71
(if you wanted to go the extra mile, you could take the $5 in Propel which is non-taxable and add in $2.50 * .06 = $.15
In this case, I will
Therefore Total Qs = $44.86
ECBs required = $50.97 - $44.86 = $6.11 Round to nearest whole dollar total = $6 ECB
OOP = $0.11 * 1.06 = $0.12
I hand the following Qs in the following order to the cashier
1. $10/50 e-mail (actually CRT, but this is hypothetical)
2. $2/10 CVS brand e-mail
3. $2/10 CVS brand CRT
4. Ask cashier to call manager up because there is a big Q that requires approval
5. 2 * $3.00 Pledge duster - mention to cashier that the second one will require override to $2.98 (this makes them feel more comfortable that you know what you are doing)
6. $5 Tylenol - mention to cashier that it will require overriding to $4.99
7. BOGO Crest - mention the $3.29 cost for the TP
8. By this time the manager is walking up
9. $14.99 Contour (and copy of prescription) mention that this is the big coupon that requires cashier entry and manager approval
10. 2 * $0.40 Palmolive IPs
11. 5 * $0.50 Propel tearpads
12. Swipe giftcard for $.12
Walk out with the following ECBs:
$2.00 Palmolive + $2.00 Propel + $14.99 Contour +$6.58 Crest + $8 Lumene Body Aktiva + $1 CVS soap = $34.57
Net ECBs = $34.57-$6 =
+$28.57 ECB Note: if you handed the $10/50 email last, you would pay have to pay tax on $35.97 ($2.16 OOP - a net OOP loss of $2.04). If you handed a $6 ECB to the cashier last, you would pay tax on $31.97. The $6 ECB would be overridden down to $4.20 (a net OOP of $1.80). If you tried to hand either of the $2/10 CVS brand Qs last, they would be adjusted to $0.44 credit and you would have to pay $1.68 OOP (of course that would be a net loss of $1.56 OOP). If you handed the $5 Tylenol Q, free Contour Q, or Pledge Q last, you would have to pay tax on $25.97 ($1.56 OOP - a net OOP loss of $1.44).
************************************************** **** END EXAMPLE ************************************************** ****
P.S. THIS METHOD IS SPECIFIC TO MICHIGAN!! Your state may vary by how (and if) they tax manufacturer coupons. However, I have been told that it works very well for MOST (but not all) states. One other thing, if you want to be diligent, you can fix the inaccuracy in step 2 by removing the coupons for non-taxable items from the adjustment calculation and adding them in separately at face value. I usually don't do this because MI taxes almost everything. The big bonus from this approach is that it will allow you to use Manu Q's against tax (again, I can only verify that it works in Michigan)