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	$91.86	9.266%	$100.3717	$100.37	$100.35	$100.40
Purchase #2	$177.78	7.327%	$190.8059	$190.81	$190.80	$190.80
Purchase #3	$137.44	5.644%	$145.1971	$145.20	$145.20	$145.20
Purchase #4	$135.38	4.439%	$141.3895	$141.39	$141.40	$141.40
Purchase #5	$231.91	10.593%	$256.4762	$256.48	$256.50	$256.50
Purchase #6	$234.43	3.617%	$242.9093	$242.91	$242.90	$242.90
Purchase #7	$52.89	13.580%	$60.0725	$60.07	$60.05	$60.10
7 purchase totals =	$1,061.69		$1,137.2222	$1,137.23	$1,137.20	$1,137.30