Jimmy. It doesn't matter that he can run simple calculations in his head, this is a matter of both security and inventory management. In a business it's important to document transactions to not only ensure no funny business occurs with funds, but to also keep an eye on supplies to turn optimal profits. Moreover, Skeet is his superior. We've all worked with frustrating people, but the simple fact remains is that Skeet has the right to manage his employees how he sees fit.
In short, Jimmy is a huge asshole who thinks his intelligence gives him the right to do whatever he wants