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	$47.52	7.564%	$51.1144	$51.11	$51.10	$51.10
Purchase #2	$26.77	5.120%	$28.1406	$28.14	$28.15	$28.10
Purchase #3	$153.50	12.127%	$172.1149	$172.11	$172.10	$172.10
Purchase #4	$155.47	11.363%	$173.1361	$173.14	$173.15	$173.10
Purchase #5	$58.82	12.316%	$66.0643	$66.06	$66.05	$66.10
Purchase #6	$53.26	11.181%	$59.215	$59.22	$59.20	$59.20
Purchase #7	$81.66	8.383%	$88.5056	$88.51	$88.50	$88.50
7 purchase totals =	$577.00		$638.2909	$638.29	$638.25	$638.20