Incorrect tax on discounted amount

[wygk]

Sub-Total: $2,985.40
Free Shipping Options (Best way): $0.00
Discount Coupon: safe11 : -$149.27
TX Sales Tax: $228.89
Total: $3,065.02


Subtotal - Discount = $2,836.13

TX sales tax = .0825, so the tax should be $233.98

Instead, it's $228.89 ! Any thoughts?