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	$52.73	11.566%	$58.8288	$58.83	$58.85	$58.80
Purchase #2	$37.55	7.352%	$40.3107	$40.31	$40.30	$40.30
Purchase #3	$6.74	11.768%	$7.5332	$7.53	$7.55	$7.50
Purchase #4	$116.34	13.672%	$132.246	$132.25	$132.25	$132.20
Purchase #5	$230.34	10.150%	$253.7195	$253.72	$253.70	$253.70
Purchase #6	$50.65	5.689%	$53.5315	$53.53	$53.55	$53.50
Purchase #7	$90.87	4.505%	$94.9637	$94.96	$94.95	$95.00
7 purchase totals =	$585.22		$641.1334	$641.13	$641.15	$641.00