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	$12.89	5.238%	$13.5652	$13.57	$13.55	$13.60
Purchase #2	$69.43	7.287%	$74.4894	$74.49	$74.50	$74.50
Purchase #3	$129.61	7.466%	$139.2867	$139.29	$139.30	$139.30
Purchase #4	$153.47	12.440%	$172.5617	$172.56	$172.55	$172.60
Purchase #5	$52.35	7.844%	$56.4563	$56.46	$56.45	$56.50
Purchase #6	$50.83	5.714%	$53.7344	$53.73	$53.75	$53.70
Purchase #7	$64.56	8.724%	$70.1922	$70.19	$70.20	$70.20
7 purchase totals =	$533.14		$580.2859	$580.29	$580.30	$580.40