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	$52.85	13.365%	$59.9134	$59.91	$59.90	$59.90
Purchase #2	$78.49	11.464%	$87.4881	$87.49	$87.50	$87.50
Purchase #3	$147.92	6.863%	$158.0717	$158.07	$158.05	$158.10
Purchase #4	$34.43	13.303%	$39.0102	$39.01	$39.00	$39.00
Purchase #5	$55.30	12.320%	$62.113	$62.11	$62.10	$62.10
Purchase #6	$50.57	11.701%	$56.4872	$56.49	$56.50	$56.50
Purchase #7	$68.98	8.161%	$74.6095	$74.61	$74.60	$74.60
7 purchase totals =	$488.54		$537.6931	$537.69	$537.65	$537.70