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	$139.96	7.508%	$150.4682	$150.47	$150.45	$150.50
Purchase #2	$226.49	11.329%	$252.1491	$252.15	$252.15	$252.10
Purchase #3	$225.26	4.680%	$235.8022	$235.80	$235.80	$235.80
Purchase #4	$11.28	8.839%	$12.277	$12.28	$12.30	$12.30
Purchase #5	$39.31	11.468%	$43.8181	$43.82	$43.80	$43.80
Purchase #6	$166.93	3.380%	$172.5722	$172.57	$172.55	$172.60
Purchase #7	$40.81	10.710%	$45.1808	$45.18	$45.20	$45.20
7 purchase totals =	$850.04		$912.2676	$912.27	$912.25	$912.30