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	$9.31	9.178%	$10.1645	$10.16	$10.15	$10.20
Purchase #2	$115.45	11.472%	$128.6944	$128.69	$128.70	$128.70
Purchase #3	$249.46	9.343%	$272.767	$272.77	$272.75	$272.80
Purchase #4	$25.35	3.550%	$26.2499	$26.25	$26.25	$26.20
Purchase #5	$89.65	10.560%	$99.117	$99.12	$99.10	$99.10
Purchase #6	$99.50	9.493%	$108.9455	$108.95	$108.95	$108.90
Purchase #7	$152.95	10.208%	$168.5631	$168.56	$168.55	$168.60
7 purchase totals =	$741.67		$814.5014	$814.50	$814.45	$814.50