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	$134.49	3.131%	$138.7009	$138.70	$138.70	$138.70
Purchase #2	$120.74	5.521%	$127.4061	$127.41	$127.40	$127.40
Purchase #3	$11.82	3.136%	$12.1907	$12.19	$12.20	$12.20
Purchase #4	$95.35	9.488%	$104.3968	$104.40	$104.40	$104.40
Purchase #5	$55.90	10.573%	$61.8103	$61.81	$61.80	$61.80
Purchase #6	$17.50	6.140%	$18.5745	$18.57	$18.55	$18.60
Purchase #7	$50.35	10.851%	$55.8135	$55.81	$55.80	$55.80
7 purchase totals =	$486.15		$518.8928	$518.89	$518.85	$518.90