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	$35.94	13.741%	$40.8785	$40.88	$40.90	$40.90
Purchase #2	$146.31	13.634%	$166.2579	$166.26	$166.25	$166.30
Purchase #3	$208.87	11.768%	$233.4498	$233.45	$233.45	$233.40
Purchase #4	$234.50	3.380%	$242.4261	$242.43	$242.45	$242.40
Purchase #5	$111.83	4.658%	$117.039	$117.04	$117.05	$117.00
Purchase #6	$126.25	3.329%	$130.4529	$130.45	$130.45	$130.50
Purchase #7	$138.47	3.338%	$143.0921	$143.09	$143.10	$143.10
7 purchase totals =	$1,002.17		$1,073.5963	$1,073.60	$1,073.65	$1,073.60