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	$124.27	11.777%	$138.9053	$138.91	$138.90	$138.90
Purchase #2	$95.79	4.545%	$100.1437	$100.14	$100.15	$100.10
Purchase #3	$90.54	11.326%	$100.7946	$100.79	$100.80	$100.80
Purchase #4	$239.31	12.466%	$269.1424	$269.14	$269.15	$269.10
Purchase #5	$232.35	10.195%	$256.0381	$256.04	$256.05	$256.00
Purchase #6	$8.62	12.162%	$9.6684	$9.67	$9.65	$9.70
Purchase #7	$222.70	13.675%	$253.1542	$253.15	$253.15	$253.20
7 purchase totals =	$1,013.58		$1,127.8467	$1,127.84	$1,127.85	$1,127.80