Tips, meaning to insure proper service. The best way to do that is to tip early and often. If you elect to take your time, you’ll enjoy lengthy waits between drinks. Working at a bar isn't table service, meaning you’re buying a bartender’s time. This means the bartender is thinking, Why would I waste time with someone who isn't tipping graciously when I can spend it with someone who's actually spending?
Like everyone else in the service industry, the absolute worst thing you can do to a bartender after they've put up with you for however long is to disrespect them via a pathetic tip. If you can’t afford to fork over a respectable amount after paying for your $3 PBR, why the hell are you out?
The industry standard for tipping is 20%—if you can’t adhere to that, please don't frequent bars. The minimum tip for anything up to $5 is $1. And don’t you dare attempt to tip with change. That's for panhandlers.