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	$26.85	4.620%	$28.0905	$28.09	$28.10	$28.10
Purchase #2	$50.88	8.756%	$55.3351	$55.34	$55.35	$55.30
Purchase #3	$47.82	5.105%	$50.2612	$50.26	$50.25	$50.30
Purchase #4	$38.62	13.655%	$43.8936	$43.89	$43.90	$43.90
Purchase #5	$107.32	3.641%	$111.2275	$111.23	$111.25	$111.20
Purchase #6	$151.83	12.525%	$170.8467	$170.85	$170.85	$170.80
Purchase #7	$48.42	4.588%	$50.6415	$50.64	$50.65	$50.60
7 purchase totals =	$471.74		$510.2961	$510.30	$510.35	$510.20