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	$238.35	7.622%	$256.517	$256.52	$256.50	$256.50
Purchase #2	$220.81	9.320%	$241.3895	$241.39	$241.40	$241.40
Purchase #3	$48.70	10.805%	$53.962	$53.96	$53.95	$54.00
Purchase #4	$66.77	12.387%	$75.0408	$75.04	$75.05	$75.00
Purchase #5	$231.77	4.638%	$242.5195	$242.52	$242.50	$242.50
Purchase #6	$139.80	13.630%	$158.8547	$158.85	$158.85	$158.90
Purchase #7	$105.64	3.280%	$109.105	$109.11	$109.10	$109.10
7 purchase totals =	$1,051.84		$1,137.3885	$1,137.39	$1,137.35	$1,137.40