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	$9.75	9.843%	$10.7097	$10.71	$10.70	$10.70
Purchase #2	$160.52	7.280%	$172.2059	$172.21	$172.20	$172.20
Purchase #3	$118.72	11.697%	$132.6067	$132.61	$132.60	$132.60
Purchase #4	$37.89	6.177%	$40.2305	$40.23	$40.25	$40.20
Purchase #5	$136.94	12.127%	$153.5467	$153.55	$153.55	$153.50
Purchase #6	$231.73	10.634%	$256.3722	$256.37	$256.35	$256.40
Purchase #7	$56.34	6.409%	$59.9508	$59.95	$59.95	$60.00
7 purchase totals =	$751.89		$825.6225	$825.63	$825.60	$825.60