I have better together installed and am using it for a buy from one category get item from other category at $5 off. It works fine alone. What doesn't work is when it is used along side the ZenCart Coupon Discount on a taxable good. I am having some problems on the checkout calculations.

Right now I am only taxing to California residents and this problem only applies to those orders that involve tax...

If the BT Discount comes after the 10% off Coupon Discount in the sort order things calculate fine it seems. However, if it comes before the coupon discount (as my client prefers) it deducts some change from the total of the coupon discount. For example:

Sub-Total: $190.00
FREE SHIPPING! (Free Shipping Only):$0.00
Matching Set Discount:-$10.00 <-Better Together
Discount Coupon: 10%OFF :-$17.92
CA TAX 8.25%: $13.36
Total: $175.44

So the Discount coupon should really be for $18.
error in price varies depending on what's in the cart...it's not always an $.08 difference.

I have no idea why this is happening. Both modules are set to:
Include tax: False
Recalculate Tax: Standard

Please help!! I've spent all day trying to figure this out and had to launch the site with the problem.