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	$137.43	11.523%	$153.2661	$153.27	$153.25	$153.30
Purchase #2	$112.83	13.248%	$127.7777	$127.78	$127.80	$127.80
Purchase #3	$206.37	12.260%	$231.671	$231.67	$231.65	$231.70
Purchase #4	$15.82	11.327%	$17.6119	$17.61	$17.60	$17.60
Purchase #5	$19.57	10.451%	$21.6153	$21.62	$21.60	$21.60
Purchase #6	$13.83	11.540%	$15.426	$15.43	$15.45	$15.40
Purchase #7	$235.40	7.542%	$253.1539	$253.15	$253.15	$253.20
7 purchase totals =	$741.25		$820.5219	$820.53	$820.50	$820.60