I suspect there may be a rounding issue somewhere in this contribution.
I had added a 5% handling fee to all shipments, and when I tried to process an order for a customer, my gateway came back with an error. I processed the order by hand, and when I added up product subtotal, shipping, and sales tax manually, the grand total came back $0.01 lower than what OSC reported as the total. I went back and removed the 5%, and everything added up.
Can someone please check? I would - but I have no idea where to even start.