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	$238.41	6.142%	$253.0531	$253.05	$253.05	$253.10
Purchase #2	$40.59	12.312%	$45.5874	$45.59	$45.60	$45.60
Purchase #3	$244.89	5.615%	$258.6406	$258.64	$258.65	$258.60
Purchase #4	$82.50	3.245%	$85.1771	$85.18	$85.20	$85.20
Purchase #5	$74.62	10.389%	$82.3723	$82.37	$82.35	$82.40
Purchase #6	$21.71	11.323%	$24.1682	$24.17	$24.15	$24.20
Purchase #7	$47.51	12.766%	$53.5751	$53.58	$53.60	$53.60
7 purchase totals =	$750.23		$802.5738	$802.58	$802.60	$802.70