I've had bills for amounts in the "few pennies" range; less than the value of the postage stamp. Back in the days when I paid via checks and snail mail, I recall on at least one (possibly more) occasion I intentionally sent a check rounded up to a dollar.

This accomplished two things. First, it threw any possible round-off-error ball back into their court. And second, it gained me the minor satisfaction of getting the last word -- forcing a refund check in a silly-small amount.