I did something similar to that the other day at the farmer’s market. The bill was something like $9.46 so I gave her a ten dollar bill and .46 in change. She had to use her calculator!! But she was very pleasant.
I, in a louder voice told him that if there was a discrepancy in what I told him I was giving him, he should have said such as he was “counting”.
Just loud enough for others in line to hear what happened.