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	$79.50	3.305%	$82.1275	$82.13	$82.15	$82.10
Purchase #2	$111.55	10.513%	$123.2773	$123.28	$123.30	$123.30
Purchase #3	$23.30	5.544%	$24.5918	$24.59	$24.60	$24.60
Purchase #4	$47.98	11.466%	$53.4814	$53.48	$53.50	$53.50
Purchase #5	$151.58	9.693%	$166.2726	$166.27	$166.25	$166.30
Purchase #6	$125.71	7.103%	$134.6392	$134.64	$134.65	$134.60
Purchase #7	$14.85	3.546%	$15.3766	$15.38	$15.40	$15.40
7 purchase totals =	$554.47		$599.7664	$599.77	$599.85	$599.80