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	$59.62	11.680%	$66.5836	$66.58	$66.60	$66.60
Purchase #2	$136.61	12.484%	$153.6644	$153.66	$153.65	$153.70
Purchase #3	$96.49	12.246%	$108.3062	$108.31	$108.30	$108.30
Purchase #4	$135.75	6.780%	$144.9539	$144.95	$144.95	$145.00
Purchase #5	$94.84	5.738%	$100.2819	$100.28	$100.30	$100.30
Purchase #6	$175.84	6.559%	$187.3733	$187.37	$187.35	$187.40
Purchase #7	$238.74	7.453%	$256.5333	$256.53	$256.55	$256.50
7 purchase totals =	$937.89		$1,017.6966	$1,017.68	$1,017.70	$1,017.80