For beers, glasses of wine, or single liquor drinks (IE rum & cokes, vodka sodas etc) that's totally fine. Regular cocktails/martinis $2 is appreciated & if the bartender is quick, makes a good drink, & is kind $2 & the rest of whatever the change was (so like $2-$3) is nice 🙂 if you have an ongoing tab at the bar, typically 20% is the norm. I never expect anything, but I appreciate your asking & I wanted to give you my insight

When I was in NYC a couple told me they’d gin me to a restaurant and the bill came to $325. They tipped $25 and waiter said if you can’t tip properly don’t tip at all so he got ZERO