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	$144.67	10.265%	$159.5204	$159.52	$159.50	$159.50
Purchase #2	$83.88	5.182%	$88.2267	$88.23	$88.25	$88.20
Purchase #3	$37.92	4.688%	$39.6977	$39.70	$39.70	$39.70
Purchase #4	$92.27	8.594%	$100.1997	$100.20	$100.20	$100.20
Purchase #5	$92.64	13.420%	$105.0723	$105.07	$105.05	$105.10
Purchase #6	$215.82	3.537%	$223.4536	$223.45	$223.45	$223.50
Purchase #7	$177.56	3.546%	$183.8563	$183.86	$183.85	$183.90
7 purchase totals =	$844.76		$900.0267	$900.03	$900.00	$900.10