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	$48.44	3.530%	$50.1499	$50.15	$50.15	$50.10
Purchase #2	$39.79	11.803%	$44.4864	$44.49	$44.50	$44.50
Purchase #3	$106.94	10.262%	$117.9142	$117.91	$117.90	$117.90
Purchase #4	$132.95	10.395%	$146.7702	$146.77	$146.75	$146.80
Purchase #5	$40.59	8.181%	$43.9107	$43.91	$43.90	$43.90
Purchase #6	$48.51	13.157%	$54.8925	$54.89	$54.90	$54.90
Purchase #7	$64.55	13.790%	$73.4514	$73.45	$73.45	$73.50
7 purchase totals =	$481.77		$531.5753	$531.57	$531.55	$531.60