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	$11.87	6.805%	$12.6778	$12.68	$12.70	$12.70
Purchase #2	$11.69	3.278%	$12.0732	$12.07	$12.05	$12.10
Purchase #3	$18.39	7.582%	$19.7843	$19.78	$19.80	$19.80
Purchase #4	$101.55	9.646%	$111.3455	$111.35	$111.35	$111.30
Purchase #5	$58.76	5.251%	$61.8455	$61.85	$61.85	$61.80
Purchase #6	$149.82	5.706%	$158.3687	$158.37	$158.35	$158.40
Purchase #7	$99.41	4.690%	$104.0723	$104.07	$104.05	$104.10
7 purchase totals =	$451.49		$480.1673	$480.17	$480.15	$480.20