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	$168.70	11.731%	$188.4902	$188.49	$188.50	$188.50
Purchase #2	$165.78	10.785%	$183.6594	$183.66	$183.65	$183.70
Purchase #3	$132.85	5.749%	$140.4875	$140.49	$140.50	$140.50
Purchase #4	$111.28	11.531%	$124.1117	$124.11	$124.10	$124.10
Purchase #5	$146.63	9.488%	$160.5423	$160.54	$160.55	$160.50
Purchase #6	$83.75	7.844%	$90.3194	$90.32	$90.30	$90.30
Purchase #7	$54.81	11.580%	$61.157	$61.16	$61.15	$61.20
7 purchase totals =	$863.80		$948.7675	$948.77	$948.75	$948.80