At a lot of places in the US, the waitstaff are paid very little, on the understanding that tips will make up a significant part of their salary. In fact, this is why they can be paid less than minimum wage. So basically, if they don't get tips, they end up in dire financial straits. And that is severely uncool. Thanks to this rubbish, my tip no longer means "here's something extra," but instead, "I'm not deliberately depriving you of what you need to feed your family."
So I try to be as sympathetic as my wallet allows. If I'm sitting down to eat, I put in at least 10% more. If the service is bad, I leave nothing. If the service is good, I might leave plenty more. I always tip the pizza guy, the barber, and the bartender well. This ensures I get warm pizza, decent cuts, and strong drinks.
Incidentally, I never leave a fractional tip. If a meal costs $8.75, a 10% rounds me up to $10. If I want to tip more for great service, I'll do it in $1 increments. Likewise, I never leave less than $1 if I decide to tip at all (unless I'm dumping spare change into a tip cup). I don't want to send the message that I'd rather count change than break out the bills, when someone at least made an effort to be friendly to me. But hey, that's just me.
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Sainte atha ma u Hrair, kan zyhlante hray u vahra ma hyaones.
My heart has joined the Thousand, for my friend stopped running today.