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	$42.55	7.158%	$45.5957	$45.60	$45.60	$45.60
Purchase #2	$86.80	3.434%	$89.7807	$89.78	$89.80	$89.80
Purchase #3	$79.29	10.500%	$87.6155	$87.62	$87.60	$87.60
Purchase #4	$6.57	13.460%	$7.4543	$7.45	$7.45	$7.50
Purchase #5	$57.35	7.680%	$61.7545	$61.75	$61.75	$61.80
Purchase #6	$196.75	12.198%	$220.7496	$220.75	$220.75	$220.70
Purchase #7	$97.72	8.181%	$105.7145	$105.71	$105.70	$105.70
7 purchase totals =	$567.03		$618.6648	$618.66	$618.65	$618.70