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	$12.55	5.317%	$13.2173	$13.22	$13.20	$13.20
Purchase #2	$61.59	11.390%	$68.6051	$68.61	$68.60	$68.60
Purchase #3	$115.91	7.575%	$124.6902	$124.69	$124.70	$124.70
Purchase #4	$48.31	13.223%	$54.698	$54.70	$54.70	$54.70
Purchase #5	$201.65	7.352%	$216.4753	$216.48	$216.50	$216.50
Purchase #6	$42.72	6.860%	$45.6506	$45.65	$45.65	$45.70
Purchase #7	$40.31	13.110%	$45.5946	$45.59	$45.60	$45.60
7 purchase totals =	$523.04		$568.9311	$568.94	$568.95	$569.00