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	$132.62	10.654%	$146.7493	$146.75	$146.75	$146.70
Purchase #2	$52.86	13.169%	$59.8211	$59.82	$59.80	$59.80
Purchase #3	$140.49	7.795%	$151.4412	$151.44	$151.45	$151.40
Purchase #4	$18.47	9.570%	$20.2376	$20.24	$20.25	$20.20
Purchase #5	$66.28	5.850%	$70.1574	$70.16	$70.15	$70.20
Purchase #6	$228.86	7.804%	$246.7202	$246.72	$246.70	$246.70
Purchase #7	$165.97	6.578%	$176.8875	$176.89	$176.90	$176.90
7 purchase totals =	$805.55		$872.0143	$872.02	$872.00	$871.90