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	$83.73	6.634%	$89.2846	$89.28	$89.30	$89.30
Purchase #2	$112.87	3.325%	$116.6229	$116.62	$116.60	$116.60
Purchase #3	$219.86	11.672%	$245.5221	$245.52	$245.50	$245.50
Purchase #4	$214.26	6.268%	$227.6898	$227.69	$227.70	$227.70
Purchase #5	$234.58	11.189%	$260.8272	$260.83	$260.85	$260.80
Purchase #6	$49.54	10.521%	$54.7521	$54.75	$54.75	$54.80
Purchase #7	$104.43	4.328%	$108.9497	$108.95	$108.95	$108.90
7 purchase totals =	$1,019.27		$1,103.6484	$1,103.64	$1,103.65	$1,103.60