Tip culture is awful, USA and Canadians including myself need to get over this "pay by donation after you've already paid" model. I'll do it but no one outside of here should lose sleep over it.

Tips should mainly be given for "better than expected" service. I tip taxi drivers, barbers and servers on a sliding scale between 10-30%, points for if it's on a Sunday night or holiday weekend, if they accommodated a larger group during a busy time, were especially personable or did specific things to help celebrate an occasion. Everything outside that and "pay before you get the service" model earns about $1-2 tips maximum from me.