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	$57.41	6.493%	$61.1376	$61.14	$61.15	$61.10
Purchase #2	$40.37	5.603%	$42.6319	$42.63	$42.65	$42.60
Purchase #3	$124.85	5.814%	$132.1088	$132.11	$132.10	$132.10
Purchase #4	$134.63	12.356%	$151.2649	$151.26	$151.25	$151.30
Purchase #5	$42.89	12.593%	$48.2911	$48.29	$48.30	$48.30
Purchase #6	$135.51	10.483%	$149.7155	$149.72	$149.70	$149.70
Purchase #7	$40.65	6.170%	$43.1581	$43.16	$43.15	$43.20
7 purchase totals =	$576.31		$628.3079	$628.31	$628.30	$628.30