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	$189.87	9.813%	$208.5019	$208.50	$208.50	$208.50
Purchase #2	$15.69	8.177%	$16.973	$16.97	$16.95	$17.00
Purchase #3	$155.34	10.800%	$172.1167	$172.12	$172.10	$172.10
Purchase #4	$249.31	5.672%	$263.4509	$263.45	$263.45	$263.50
Purchase #5	$154.26	12.518%	$173.5703	$173.57	$173.55	$173.60
Purchase #6	$81.55	11.116%	$90.6151	$90.62	$90.60	$90.60
Purchase #7	$37.53	13.603%	$42.6352	$42.64	$42.65	$42.60
7 purchase totals =	$883.55		$967.8631	$967.87	$967.80	$967.90