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	$78.53	13.532%	$89.1567	$89.16	$89.15	$89.20
Purchase #2	$11.97	5.204%	$12.5929	$12.59	$12.60	$12.60
Purchase #3	$154.86	6.725%	$165.2743	$165.27	$165.25	$165.30
Purchase #4	$106.64	12.721%	$120.2057	$120.21	$120.20	$120.20
Purchase #5	$154.45	9.795%	$169.5784	$169.58	$169.60	$169.60
Purchase #6	$56.52	7.863%	$60.9642	$60.96	$60.95	$61.00
Purchase #7	$101.49	9.805%	$111.4411	$111.44	$111.45	$111.40
7 purchase totals =	$664.46		$729.2133	$729.21	$729.20	$729.30