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	$216.93	11.547%	$241.9789	$241.98	$242.00	$242.00
Purchase #2	$132.60	7.205%	$142.1538	$142.15	$142.15	$142.20
Purchase #3	$122.50	12.516%	$137.8321	$137.83	$137.85	$137.80
Purchase #4	$48.82	3.745%	$50.6483	$50.65	$50.65	$50.60
Purchase #5	$204.69	12.149%	$229.5578	$229.56	$229.55	$229.60
Purchase #6	$139.95	13.310%	$158.5773	$158.58	$158.60	$158.60
Purchase #7	$175.31	8.561%	$190.3183	$190.32	$190.30	$190.30
7 purchase totals =	$1,040.80		$1,151.0665	$1,151.07	$1,151.10	$1,151.10