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	$242.54	13.315%	$274.8342	$274.83	$274.85	$274.80
Purchase #2	$191.68	3.667%	$198.7089	$198.71	$198.70	$198.70
Purchase #3	$39.49	8.412%	$42.8119	$42.81	$42.80	$42.80
Purchase #4	$86.45	9.738%	$94.8685	$94.87	$94.85	$94.90
Purchase #5	$67.96	4.760%	$71.1949	$71.19	$71.20	$71.20
Purchase #6	$214.60	11.249%	$238.7404	$238.74	$238.75	$238.70
Purchase #7	$220.94	9.390%	$241.6863	$241.69	$241.70	$241.70
7 purchase totals =	$1,063.66		$1,162.8451	$1,162.84	$1,162.85	$1,162.80