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	$64.43	3.170%	$66.4724	$66.47	$66.45	$66.50
Purchase #2	$247.32	7.323%	$265.4312	$265.43	$265.45	$265.40
Purchase #3	$39.90	12.521%	$44.8959	$44.90	$44.90	$44.90
Purchase #4	$19.55	11.446%	$21.7877	$21.79	$21.80	$21.80
Purchase #5	$178.34	4.130%	$185.7054	$185.71	$185.70	$185.70
Purchase #6	$157.42	9.530%	$172.4221	$172.42	$172.40	$172.40
Purchase #7	$241.68	3.851%	$250.9871	$250.99	$251.00	$251.00
7 purchase totals =	$948.64		$1,007.7018	$1,007.71	$1,007.70	$1,007.70