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	$26.94	12.169%	$30.2183	$30.22	$30.20	$30.20
Purchase #2	$241.95	5.341%	$254.8725	$254.87	$254.85	$254.90
Purchase #3	$60.56	3.800%	$62.8613	$62.86	$62.85	$62.90
Purchase #4	$66.94	9.820%	$73.5135	$73.51	$73.50	$73.50
Purchase #5	$235.51	9.821%	$258.6394	$258.64	$258.65	$258.60
Purchase #6	$108.27	3.344%	$111.8905	$111.89	$111.90	$111.90
Purchase #7	$13.93	10.804%	$15.435	$15.44	$15.45	$15.40
7 purchase totals =	$754.10		$807.4305	$807.43	$807.40	$807.40