Tipping people for their services is a common practice in the USA but it seems the rules seem to be unspoken but understood.

https://time.com/5404475/history-tipping-american-restaurants-civil-war/

https://www.qantas.com/travelinsider/en/travel-tips/gratuities-and-tipping-in-america.html

https://www.bankrate.com/personal-finance/smart-money/a-cheat-sheet-on-tipping-dos-and-donts/