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	$100.25	6.150%	$106.4154	$106.42	$106.40	$106.40
Purchase #2	$105.66	8.240%	$114.3664	$114.37	$114.35	$114.40
Purchase #3	$150.49	13.147%	$170.2749	$170.27	$170.25	$170.30
Purchase #4	$46.61	8.521%	$50.5816	$50.58	$50.60	$50.60
Purchase #5	$249.77	10.146%	$275.1117	$275.11	$275.10	$275.10
Purchase #6	$80.67	10.521%	$89.1573	$89.16	$89.15	$89.20
Purchase #7	$93.45	11.184%	$103.9014	$103.90	$103.90	$103.90
7 purchase totals =	$826.90		$909.8087	$909.81	$909.75	$909.90