Very strange coupon behaviour

I store I support is trying to make a coupon for $5 for purchases over $30,
it seems to work fine and the details are correct in the admin, but when actually redeeming the coupon it changes to $5.05.

It's in the Aust. GST tax zone (10%) but the percentage it's off by doesn't match that, nor does it match any currency setting discrepancies (I checked after updating the conversion rates and there was no change).

Please help!

What is you default currency set to?

it's AUD

that shouldn't matter because it's clearly not being converted to another currency, i've checked a test order's totals before and after an exchange rate update and the discount amount is always incorrect.
i know it's not a db error as i have looked at the value with phpmyadmin and it shows the correct amounts.

also tried with a new coupon for 6$ this time, the amount shown at checkout is $6.07

if it was a tax problem it would be $6.60 or $5.45 or something, becuase the only tax set in the store is a %10 gst

Hi, I am also having the same kind of problem. I want to give certain customers a full discount on a specific product thats priced at say $20.00. I created a coupon of $20.00 but when I enter it at the check out it shows a difference of -$0.01. This doesn't make any sense to me. Any help?

Please post the settings you are using for the coupon calculations in the Admin> Modules> Order Total, also the totals of the merchandise from the order confirmation where you are seeing a problem.

Here are the settings that I am using...

Discount Coupon

This module is installed
true

Sort Order
280

Include Shipping
false

Include Tax
false

Re-calculate Tax
Standard

Tax Class
--none--

My settings are exactly the same as malan's but the discrepancy is more than that.

This is how it is displayed at the checkout...

Shopping Cart Contents

Qty. Item Name Total
1 x Private Pilot's License Ground School R295.00

Sub-Total: R295.00

Free Shipping: R0.00

Discount Coupon: test12345678: -R295.00

Total: R-0.01

Final Step

• continue to confirm your order. Thank you!

What version of Zen Cart are you using? Is the coupon restricted to that particular product?

Version 1.3.7.1

I did restrict it to that specific product but I also tried it without ristrictions. Same result.