Not Quite Registering

(A customer pays with a fifty-dollar bill. Spotting it, the pharmacist on duty grabs his wallet and asks the cashier to give him the fifty for two twenties and a ten.)

Coworker: “I can’t do that!”

Me: “Why not? He’s giving you $50 for $50.”

Coworker: “But my till will be wrong!”

Me: “How? You take out the fifty, and put in two twenties and the ten. The totals are still the same.”

Coworker: “But I won’t have the fifty, and the register will KNOW!”