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	$133.65	3.344%	$138.1193	$138.12	$138.10	$138.10
Purchase #2	$23.43	13.477%	$26.5877	$26.59	$26.60	$26.60
Purchase #3	$99.65	10.240%	$109.8542	$109.85	$109.85	$109.90
Purchase #4	$177.25	4.460%	$185.1554	$185.16	$185.15	$185.20
Purchase #5	$75.97	8.733%	$82.6045	$82.60	$82.60	$82.60
Purchase #6	$140.82	4.350%	$146.9457	$146.95	$146.95	$146.90
Purchase #7	$123.85	10.698%	$137.0995	$137.10	$137.10	$137.10
7 purchase totals =	$774.62		$826.3663	$826.37	$826.35	$826.40