strange rounding error when filling backorders

Has anyone else ran into this issue:

You backorder an item on a transaction and tender the transaction. Later you fill the backorder but when you tender out, there is $0.01 due because the tax on the transaction is $0.01 different for the item in question, than it was on the original receipt that contained the backorder?? I've had this happen three times now and was wonder if this is happening to anyone else.

Thanks Kevin