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	$170.30	7.548%	$183.1542	$183.15	$183.15	$183.20
Purchase #2	$88.34	13.610%	$100.3631	$100.36	$100.35	$100.40
Purchase #3	$204.45	5.816%	$216.3408	$216.34	$216.35	$216.30
Purchase #4	$155.98	11.158%	$173.3842	$173.38	$173.40	$173.40
Purchase #5	$61.76	6.477%	$65.7602	$65.76	$65.75	$65.80
Purchase #6	$161.28	8.248%	$174.5824	$174.58	$174.60	$174.60
Purchase #7	$32.95	13.433%	$37.3762	$37.38	$37.40	$37.40
7 purchase totals =	$875.06		$950.9611	$950.95	$951.00	$951.10