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	$115.52	5.527%	$121.9048	$121.90	$121.90	$121.90
Purchase #2	$95.42	10.156%	$105.1109	$105.11	$105.10	$105.10
Purchase #3	$35.91	13.296%	$40.6846	$40.68	$40.70	$40.70
Purchase #4	$5.58	13.521%	$6.3345	$6.33	$6.35	$6.30
Purchase #5	$153.32	11.446%	$170.869	$170.87	$170.85	$170.90
Purchase #6	$104.67	6.244%	$111.2056	$111.21	$111.20	$111.20
Purchase #7	$16.59	3.839%	$17.2269	$17.23	$17.25	$17.20
7 purchase totals =	$527.01		$573.3363	$573.33	$573.35	$573.30