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	$44.66	4.540%	$46.6876	$46.69	$46.70	$46.70
Purchase #2	$152.98	8.253%	$165.6054	$165.61	$165.60	$165.60
Purchase #3	$164.64	6.395%	$175.1687	$175.17	$175.15	$175.20
Purchase #4	$151.46	13.588%	$172.0404	$172.04	$172.05	$172.00
Purchase #5	$36.44	10.636%	$40.3158	$40.32	$40.30	$40.30
Purchase #6	$47.70	6.472%	$50.7871	$50.79	$50.80	$50.80
Purchase #7	$153.64	11.205%	$170.8554	$170.86	$170.85	$170.90
7 purchase totals =	$751.52		$821.4604	$821.48	$821.45	$821.50