Hospital Cashier Question:

At Macy’s, a customer got quite antsy when he realized that he did not get the change that he was supposed to. He gave me a $100 bill and I was required to return $20 to him but accidentally gave him $10. He got very upset and asked to see a supervisor. I apologized but did not offer too much of an explanation of my error as I somehow gauged he was too upset to listen to me. I called my supervisor before the situation got out of hand.