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	$214.32	12.180%	$240.4242	$240.42	$240.40	$240.40
Purchase #2	$52.94	6.699%	$56.4865	$56.49	$56.50	$56.50
Purchase #3	$126.25	10.482%	$139.4835	$139.48	$139.50	$139.50
Purchase #4	$101.53	11.776%	$113.4862	$113.49	$113.50	$113.50
Purchase #5	$242.89	13.456%	$275.5733	$275.57	$275.55	$275.60
Purchase #6	$60.81	6.425%	$64.717	$64.72	$64.70	$64.70
Purchase #7	$173.35	11.551%	$193.3737	$193.37	$193.35	$193.40
7 purchase totals =	$972.09		$1,083.5444	$1,083.54	$1,083.50	$1,083.60