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	$10.70	6.598%	$11.406	$11.41	$11.40	$11.40
Purchase #2	$228.25	9.498%	$249.9292	$249.93	$249.95	$249.90
Purchase #3	$42.88	13.305%	$48.5852	$48.59	$48.60	$48.60
Purchase #4	$111.29	10.169%	$122.6071	$122.61	$122.60	$122.60
Purchase #5	$13.67	13.172%	$15.4706	$15.47	$15.45	$15.50
Purchase #6	$208.57	6.244%	$221.5931	$221.59	$221.60	$221.60
Purchase #7	$211.84	5.102%	$222.6481	$222.65	$222.65	$222.60
7 purchase totals =	$827.20		$892.2393	$892.25	$892.25	$892.20