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	$51.57	7.472%	$55.4233	$55.42	$55.40	$55.40
Purchase #2	$111.89	12.265%	$125.6133	$125.61	$125.60	$125.60
Purchase #3	$190.69	8.150%	$206.2312	$206.23	$206.25	$206.20
Purchase #4	$143.60	11.388%	$159.9532	$159.95	$159.95	$160.00
Purchase #5	$144.77	12.518%	$162.8923	$162.89	$162.90	$162.90
Purchase #6	$45.65	5.554%	$48.1854	$48.19	$48.20	$48.20
Purchase #7	$150.33	4.241%	$156.7055	$156.71	$156.70	$156.70
7 purchase totals =	$838.50		$915.0042	$915.00	$915.00	$915.00