I'm currently using ZC 1.3.0.2, but I just confirmed this same thing happens with ZC 1.3.5. I didn't have this problem when I had 1.2.6d

Current configuration for Modules>Order Total>Discount Coupon
Include Tax in Calculation: False
Recalculate Tax: Standard


--Example--
Subtotal: $78.14
Discount 5%: -$3.91
Sales Tax 8.25%: $5.81

Sales tax is incorrect, it should be $6.12. In the above example it's also taking 5% off what should be the correct sales tax amount.
The configuration 'include tax in calculation: False' and 'Recalculate tax: Standard' worked just fine in ZC 1.2.6

So my question is, what should be the proper configuration to accomplish this or is there a bug? I have tried several combinations and the one that seems to almost work is:
Include Tax in Calculation: False
Recalculate Tax: Credit Note
Tax Class
Use the following tax class when treating Discount Coupon as Credit Note: Taxable Goods

So this gives me 'Sales Tax 8.25%: $6.13', which is still off by 1 cent.