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	$83.98	7.648%	$90.4028	$90.40	$90.40	$90.40
Purchase #2	$59.84	11.485%	$66.7126	$66.71	$66.70	$66.70
Purchase #3	$196.34	10.286%	$216.5355	$216.54	$216.55	$216.50
Purchase #4	$80.58	10.307%	$88.8854	$88.89	$88.90	$88.90
Purchase #5	$107.52	3.142%	$110.8983	$110.90	$110.90	$110.90
Purchase #6	$228.40	4.485%	$238.6437	$238.64	$238.65	$238.60
Purchase #7	$144.66	7.801%	$155.9449	$155.94	$155.95	$155.90
7 purchase totals =	$901.32		$968.0232	$968.02	$968.05	$967.90