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	$152.28	13.578%	$172.9566	$172.96	$172.95	$173.00
Purchase #2	$99.54	11.845%	$111.3305	$111.33	$111.35	$111.30
Purchase #3	$241.30	12.813%	$272.2178	$272.22	$272.20	$272.20
Purchase #4	$156.39	7.344%	$167.8753	$167.88	$167.90	$167.90
Purchase #5	$11.26	11.477%	$12.5523	$12.55	$12.55	$12.60
Purchase #6	$183.67	10.851%	$203.6	$203.60	$203.60	$203.60
Purchase #7	$10.27	5.290%	$10.8133	$10.81	$10.80	$10.80
7 purchase totals =	$854.71		$951.3458	$951.35	$951.35	$951.40