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	$135.66	11.680%	$151.5051	$151.51	$151.50	$151.50
Purchase #2	$204.51	13.106%	$231.3131	$231.31	$231.30	$231.30
Purchase #3	$28.38	11.720%	$31.7061	$31.71	$31.70	$31.70
Purchase #4	$110.28	12.152%	$123.6812	$123.68	$123.70	$123.70
Purchase #5	$132.83	8.283%	$143.8323	$143.83	$143.85	$143.80
Purchase #6	$146.43	8.192%	$158.4255	$158.43	$158.45	$158.40
Purchase #7	$68.83	9.845%	$75.6063	$75.61	$75.60	$75.60
7 purchase totals =	$826.92		$916.0696	$916.08	$916.10	$916.00