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	$18.71	10.606%	$20.6944	$20.69	$20.70	$20.70
Purchase #2	$151.85	12.136%	$170.2785	$170.28	$170.30	$170.30
Purchase #3	$25.44	10.671%	$28.1547	$28.15	$28.15	$28.20
Purchase #4	$44.85	7.594%	$48.2559	$48.26	$48.25	$48.30
Purchase #5	$71.55	10.783%	$79.2652	$79.27	$79.25	$79.30
Purchase #6	$98.72	13.139%	$111.6908	$111.69	$111.70	$111.70
Purchase #7	$65.84	9.637%	$72.185	$72.19	$72.20	$72.20
7 purchase totals =	$476.96		$530.5245	$530.53	$530.55	$530.70