To answer questions from a previous now closed thread, yes you tip bartenders when you are sitting at the bar. If you are paying for each drink as you go along, then you can tip each time. Or you can wait until the end and leave the money on the bar by your glass. They will know what it's for.
If you are running a tab and paying the bill at the end, then you tip on the entire amount at that time (cash or credit card) just like you would for a meal served at a table.