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!