15 years ago, or so, I had a similar problem. After ringing up the order, gave the girl the odd change. She didn't cry but, called the teen-aged shift manager over to help and, he had to use a calculator to figure it out.
Now that they take credit cards, we no longer have that problem. However, since I only took 2 yrs of LATIN in High school, and flunked it, I still end up with random bags of food that have no relation to my order.