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	$9.69	11.495%	$10.8039	$10.80	$10.80	$10.80
Purchase #2	$220.50	6.391%	$234.5922	$234.59	$234.60	$234.60
Purchase #3	$65.77	10.402%	$72.6114	$72.61	$72.60	$72.60
Purchase #4	$240.94	7.447%	$258.8828	$258.88	$258.90	$258.90
Purchase #5	$237.90	8.656%	$258.4926	$258.49	$258.50	$258.50
Purchase #6	$104.43	6.588%	$111.3098	$111.31	$111.30	$111.30
Purchase #7	$126.57	4.313%	$132.029	$132.03	$132.05	$132.00
7 purchase totals =	$1,005.80		$1,078.7217	$1,078.71	$1,078.75	$1,078.70