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	$9.43	12.468%	$10.6057	$10.61	$10.60	$10.60
Purchase #2	$15.67	11.447%	$17.4637	$17.46	$17.45	$17.50
Purchase #3	$159.30	8.325%	$172.5617	$172.56	$172.55	$172.60
Purchase #4	$63.88	11.834%	$71.4396	$71.44	$71.45	$71.40
Purchase #5	$199.67	11.610%	$222.8517	$222.85	$222.85	$222.90
Purchase #6	$58.49	7.118%	$62.6533	$62.65	$62.65	$62.70
Purchase #7	$74.92	5.665%	$79.1642	$79.16	$79.15	$79.20
7 purchase totals =	$581.36		$636.7399	$636.73	$636.70	$636.90