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	$51.39	9.863%	$56.4586	$56.46	$56.45	$56.50
Purchase #2	$167.51	6.370%	$178.1804	$178.18	$178.20	$178.20
Purchase #3	$123.66	4.620%	$129.3731	$129.37	$129.35	$129.40
Purchase #4	$237.97	11.635%	$265.6578	$265.66	$265.65	$265.70
Purchase #5	$78.92	13.422%	$89.5126	$89.51	$89.50	$89.50
Purchase #6	$138.61	3.292%	$143.173	$143.17	$143.15	$143.20
Purchase #7	$241.85	13.462%	$274.4078	$274.41	$274.40	$274.40
7 purchase totals =	$1,039.91		$1,136.7633	$1,136.76	$1,136.70	$1,136.90