But the 'going rate' for buffets in North America isn't 15%, based on the responses on this thread. And it certainly isn't that in most of the rest of the world, which is why I asked what is the norm in North America.

I'm not going to quibble over 0,50 cents, which is the difference between 10/15/20 percent in my example, but it also wasn't a buffet. Next time I eat there I'll leave a dollar plus round up to the next dollar, which again on a $10 total is marginal.

I don't eat at buffets except for the ones in hotel restaurants (which tend to be relatively simple bread/cereal/yoghurt/jams/fruit and possibly eggs). Nor do I eat at budget, cheap food places such as Golden Corral, or the places where people overindulge on prime rib and lobster tails such as found on the giant brunch or dinner buffets in North America.

At the breakfast buffets where I do eat outside North America, I just round up to the nearest amount.

Thanks to those of you who replied re tipping at buffets in North America.