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	$122.56	4.854%	$128.5091	$128.51	$128.50	$128.50
Purchase #2	$102.35	8.693%	$111.2473	$111.25	$111.25	$111.20
Purchase #3	$233.91	9.609%	$256.3864	$256.39	$256.40	$256.40
Purchase #4	$241.88	12.662%	$272.5068	$272.51	$272.50	$272.50
Purchase #5	$107.72	13.615%	$122.3861	$122.39	$122.40	$122.40
Purchase #6	$95.46	3.851%	$99.1362	$99.14	$99.15	$99.10
Purchase #7	$247.66	7.189%	$265.4643	$265.46	$265.45	$265.50
7 purchase totals =	$1,151.54		$1,255.6362	$1,255.65	$1,255.65	$1,255.60