I am a cashier at a gas station in California and I recently had a customer put me in this situation. They prepaid for $50 in gas with a fifty dollar bill and filled their car. They had $19 in change. When the customer came in for their change, I gave them a ten, a five, and four singles.
The customer handed me back the ten and the five and told me she wanted all her change in singles. I told her I could not do that because that would leave me very low in singles (only three left). I said the best I could do is take the five back in exchange for five singles. She refused and told me because I had nineteen singles in my register, I was legally obligated to give her change all in singles if she wished. By then, there was a line of customers building, so I didn't want to argue any further and gave her all singles.
So was she correct? Does she have the legal right to receive her change in any denomination if the cashier has enough to cover it? Hypothetically, if she wanted all her $19 of change in pennies, do I have to give it to her in that denomination if I had $19 worth of penny rolls in my register?