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	$72.33	12.219%	$81.168	$81.17	$81.15	$81.20
Purchase #2	$202.66	13.829%	$230.6859	$230.69	$230.70	$230.70
Purchase #3	$128.67	10.745%	$142.4956	$142.50	$142.50	$142.50
Purchase #4	$214.43	6.763%	$228.9319	$228.93	$228.95	$228.90
Purchase #5	$140.37	8.776%	$152.6889	$152.69	$152.70	$152.70
Purchase #6	$177.40	13.810%	$201.8989	$201.90	$201.90	$201.90
Purchase #7	$149.79	5.830%	$158.5228	$158.52	$158.50	$158.50
7 purchase totals =	$1,085.65		$1,196.3920	$1,196.40	$1,196.40	$1,196.40