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	$103.30	4.702%	$108.1572	$108.16	$108.15	$108.20
Purchase #2	$46.93	7.601%	$50.4971	$50.50	$50.50	$50.50
Purchase #3	$116.83	12.652%	$131.6113	$131.61	$131.60	$131.60
Purchase #4	$140.72	12.554%	$158.386	$158.39	$158.40	$158.40
Purchase #5	$230.81	9.844%	$253.5309	$253.53	$253.55	$253.50
Purchase #6	$20.57	7.754%	$22.165	$22.17	$22.15	$22.20
Purchase #7	$9.86	9.485%	$10.7952	$10.80	$10.80	$10.80
7 purchase totals =	$669.02		$735.1427	$735.16	$735.15	$735.20