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	$216.35	13.836%	$246.2842	$246.28	$246.30	$246.30
Purchase #2	$166.82	12.712%	$188.0262	$188.03	$188.05	$188.00
Purchase #3	$212.45	4.668%	$222.3672	$222.37	$222.35	$222.40
Purchase #4	$11.89	8.211%	$12.8663	$12.87	$12.85	$12.90
Purchase #5	$172.72	7.626%	$185.8916	$185.89	$185.90	$185.90
Purchase #6	$6.75	13.472%	$7.6594	$7.66	$7.65	$7.70
Purchase #7	$114.58	3.329%	$118.3944	$118.39	$118.40	$118.40
7 purchase totals =	$901.56		$981.4893	$981.49	$981.50	$981.60