Saying "keep the change" at the farmers' market

Pay in cash, and round up to the nearest dollar. I overheard the gal in front of me at the apple stand say this, and it was a revelation. What an elegant way to say thank you and not make a big deal about it.

Also, by the third visit to a stand or stall, introduce yourself! I'm an introvert, and it's hard, I know, but it's also very humanizing and fun. I've met some interesting and kind people this way.