Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$216.53	12.821%	$244.2913	$244.29	$244.30	$244.30
Purchase #2	$78.70	5.353%	$82.9128	$82.91	$82.90	$82.90
Purchase #3	$132.55	3.477%	$137.1588	$137.16	$137.15	$137.20
Purchase #4	$43.35	8.771%	$47.1522	$47.15	$47.15	$47.20
Purchase #5	$166.46	6.153%	$176.7023	$176.70	$176.70	$176.70
Purchase #6	$18.43	13.229%	$20.8681	$20.87	$20.85	$20.90
Purchase #7	$238.90	12.659%	$269.1424	$269.14	$269.15	$269.10
7 purchase totals =	$894.92		$978.2279	$978.22	$978.20	$978.30