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	$151.42	4.699%	$158.5352	$158.54	$158.55	$158.50
Purchase #2	$108.61	6.853%	$116.053	$116.05	$116.05	$116.10
Purchase #3	$26.89	5.264%	$28.3055	$28.31	$28.30	$28.30
Purchase #4	$171.61	11.171%	$190.7806	$190.78	$190.80	$190.80
Purchase #5	$47.68	7.243%	$51.1335	$51.13	$51.15	$51.10
Purchase #6	$108.57	10.162%	$119.6029	$119.60	$119.60	$119.60
Purchase #7	$6.93	10.778%	$7.6769	$7.68	$7.70	$7.70
7 purchase totals =	$621.71		$672.0876	$672.09	$672.15	$672.10