When I was 19 I worked at a very busy convenience store. When the boss trained me, he trained me to NOT punch in the amount tendered (that is, the amount the customer gives me) into the cash register. Instead, I was to count the change up to the amount tendered. "When you get used to it, it's much faster" he said. I was very skeptical, but he was definitely right. After a couple of shifts, I did indeed find it much faster make change that way.