During checkout, I have discovered a circumstance when Gift Certificate does not require payment information when shipping to an in-state address (charging local sales tax).

If I apply a lesser Gift Certificate amount than the total purchase, checkout allows me to Confirm My Order when full payment has not been met. In other words, I am NOT prompted for a payment method when the Gift Certificate apply amount is close to the order total. This means an order can be completed without full payment.

Gift Certificate balance: $100
Order Total: 64.58
Apply Amount: $64.50
Confirm Order Total: $0.08

On the other hand, if the Gift Certificate Apply Amount is only $50, checkout DOES prompt for an alternate payment method.

The breakpoint seems to be $0.50 - if the GC apply amount is $0.50 less than the order total, I get prompted for payment information. If the GC apply amount is $0.01 - $0.49 less than the order total, I do NOT get prompted for payment information.

I'm using Zen Cart 1.39d and Local Sales Tax mod 2.4
Local Sales Taxes are set up by zip code.

I posted this under Gift Certificates, but Ajeh could not duplicate and suggested posting here. Please HELP!