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	$228.81	11.873%	$255.9766	$255.98	$256.00	$256.00
Purchase #2	$100.85	11.194%	$112.1391	$112.14	$112.15	$112.10
Purchase #3	$221.95	4.257%	$231.3984	$231.40	$231.40	$231.40
Purchase #4	$197.49	11.366%	$219.9367	$219.94	$219.95	$219.90
Purchase #5	$65.55	8.113%	$70.8681	$70.87	$70.85	$70.90
Purchase #6	$244.63	12.196%	$274.4651	$274.47	$274.45	$274.50
Purchase #7	$241.43	5.792%	$255.4136	$255.41	$255.40	$255.40
7 purchase totals =	$1,300.71		$1,420.1976	$1,420.21	$1,420.20	$1,420.20