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	$230.92	10.630%	$255.4668	$255.47	$255.45	$255.50
Purchase #2	$235.89	5.438%	$248.7177	$248.72	$248.70	$248.70
Purchase #3	$107.64	11.724%	$120.2597	$120.26	$120.25	$120.30
Purchase #4	$40.81	10.694%	$45.1742	$45.17	$45.15	$45.20
Purchase #5	$80.29	3.196%	$82.8561	$82.86	$82.85	$82.90
Purchase #6	$131.26	7.797%	$141.4943	$141.49	$141.50	$141.50
Purchase #7	$250.78	3.835%	$260.3974	$260.40	$260.40	$260.40
7 purchase totals =	$1,077.59		$1,154.3662	$1,154.37	$1,154.30	$1,154.50