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	$242.37	5.452%	$255.584	$255.58	$255.60	$255.60
Purchase #2	$88.45	11.675%	$98.7765	$98.78	$98.80	$98.80
Purchase #3	$140.45	10.128%	$154.6748	$154.67	$154.65	$154.70
Purchase #4	$103.33	9.491%	$113.1371	$113.14	$113.15	$113.10
Purchase #5	$70.26	13.174%	$79.5161	$79.52	$79.50	$79.50
Purchase #6	$55.28	8.326%	$59.8826	$59.88	$59.90	$59.90
Purchase #7	$125.80	10.850%	$139.4493	$139.45	$139.45	$139.40
7 purchase totals =	$825.94		$901.0204	$901.02	$901.05	$901.00