My first job was running a register. For me, the people who added change to the money after I had entered it into the register flustered me. Especially if they wanted to round to the nearest quarter so they did not get back small coins. I also had people who would hand me money and inform me how much change they needed and they were trying to rip me off. I can do math just fine, but I might need a pencil and paper. When there were impatient people waiting in a line and a manager watching and all the other distractions, I just froze. I was very glad when I was able to quit that job.