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	$5.71	10.238%	$6.2946	$6.29	$6.30	$6.30
Purchase #2	$214.49	4.300%	$223.7131	$223.71	$223.70	$223.70
Purchase #3	$149.34	5.803%	$158.0062	$158.01	$158.00	$158.00
Purchase #4	$128.38	13.766%	$146.0528	$146.05	$146.05	$146.10
Purchase #5	$91.85	3.165%	$94.7571	$94.76	$94.75	$94.80
Purchase #6	$67.89	9.245%	$74.1664	$74.17	$74.15	$74.20
Purchase #7	$10.38	11.820%	$11.6069	$11.61	$11.60	$11.60
7 purchase totals =	$668.04		$714.5971	$714.60	$714.55	$714.70