“Keep the change” has a benefit to both parties - no need to spend time waiting for change to be counted or carrying it round

Colleague of mine left a new generator with his fixer in the Phillipenes when there was a massive hurricane a decade ago. He could the value of it was minimal once the time and money to ship it back to Europe was counted, reality was they needed the generator on site. Could be argued it’s not a bribe/tip/gift.

Giving money directly for services rendered could be a bribe, could be paying him on the side (for more hours for example), could attract tax problems etc.

Buying him dinner would be different.