Addendum.

I've noticed every once in a while that some (South Asian from South Asia) customers round up the bill to the nearest dollar, whether it's a $17+ bill or a $53+ one, leaving less than a dollar in change for all of the service.

I wonder, where are they getting this from?

Is this from their own country, or is it from another country they've been in, or is this something they've come up with on their own?

The last seems improbable, since multiple people have done it -- that is, unless they all arrived at the same solution where they "tip" at minimum cost to themselves.

Sometimes, if it's a table with that kind of vibe and I don't recognize them -- you want to know how they tip if they're repeat, since you deprioritize them if they don't tip! -- I just don't even look at the bill.

Like, I just don't want to know.