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	$63.34	3.388%	$65.486	$65.49	$65.50	$65.50
Purchase #2	$68.89	12.262%	$77.3373	$77.34	$77.35	$77.30
Purchase #3	$122.81	13.499%	$139.3881	$139.39	$139.40	$139.40
Purchase #4	$94.63	6.693%	$100.9636	$100.96	$100.95	$101.00
Purchase #5	$223.62	10.874%	$247.9364	$247.94	$247.95	$247.90
Purchase #6	$37.28	4.548%	$38.9755	$38.98	$39.00	$39.00
Purchase #7	$10.86	11.211%	$12.0775	$12.08	$12.10	$12.10
7 purchase totals =	$621.43		$682.1644	$682.18	$682.25	$682.20