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	$153.31	8.793%	$166.7905	$166.79	$166.80	$166.80
Purchase #2	$156.99	11.244%	$174.642	$174.64	$174.65	$174.60
Purchase #3	$140.38	4.409%	$146.5694	$146.57	$146.55	$146.60
Purchase #4	$12.91	10.179%	$14.2241	$14.22	$14.20	$14.20
Purchase #5	$223.82	4.522%	$233.9411	$233.94	$233.95	$233.90
Purchase #6	$83.49	8.533%	$90.6142	$90.61	$90.60	$90.60
Purchase #7	$83.26	8.341%	$90.2047	$90.20	$90.20	$90.20
7 purchase totals =	$854.16		$916.9860	$916.97	$916.95	$916.90