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	$65.50	12.451%	$73.6554	$73.66	$73.65	$73.70
Purchase #2	$100.63	10.530%	$111.2263	$111.23	$111.25	$111.20
Purchase #3	$55.53	13.619%	$63.0926	$63.09	$63.10	$63.10
Purchase #4	$121.92	10.396%	$134.5948	$134.59	$134.60	$134.60
Purchase #5	$176.83	7.489%	$190.0728	$190.07	$190.05	$190.10
Purchase #6	$127.73	11.119%	$141.9323	$141.93	$141.95	$141.90
Purchase #7	$102.60	5.137%	$107.8706	$107.87	$107.85	$107.90
7 purchase totals =	$750.74		$822.4448	$822.44	$822.45	$822.50