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	$9.60	11.561%	$10.7099	$10.71	$10.70	$10.70
Purchase #2	$80.77	8.763%	$87.8479	$87.85	$87.85	$87.80
Purchase #3	$131.73	7.433%	$141.5215	$141.52	$141.50	$141.50
Purchase #4	$28.97	10.227%	$31.9328	$31.93	$31.95	$31.90
Purchase #5	$91.81	8.388%	$99.511	$99.51	$99.50	$99.50
Purchase #6	$93.49	7.148%	$100.1727	$100.17	$100.15	$100.20
Purchase #7	$75.34	3.450%	$77.9392	$77.94	$77.95	$77.90
7 purchase totals =	$511.71		$549.6350	$549.63	$549.60	$549.50