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	$65.40	12.411%	$73.5168	$73.52	$73.50	$73.50
Purchase #2	$139.54	10.447%	$154.1177	$154.12	$154.10	$154.10
Purchase #3	$172.46	13.795%	$196.2509	$196.25	$196.25	$196.30
Purchase #4	$28.30	13.871%	$32.2255	$32.23	$32.25	$32.20
Purchase #5	$208.68	4.325%	$217.7054	$217.71	$217.70	$217.70
Purchase #6	$61.64	12.749%	$69.4985	$69.50	$69.50	$69.50
Purchase #7	$153.83	4.429%	$160.6431	$160.64	$160.65	$160.60
7 purchase totals =	$829.85		$903.9579	$903.97	$903.95	$903.90