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	$30.53	8.267%	$33.0539	$33.05	$33.05	$33.10
Purchase #2	$137.67	4.437%	$143.7784	$143.78	$143.80	$143.80
Purchase #3	$59.31	11.656%	$66.2232	$66.22	$66.20	$66.20
Purchase #4	$61.89	5.750%	$65.4487	$65.45	$65.45	$65.40
Purchase #5	$46.55	8.403%	$50.4616	$50.46	$50.45	$50.50
Purchase #6	$74.33	5.861%	$78.6865	$78.69	$78.70	$78.70
Purchase #7	$81.79	10.619%	$90.4753	$90.48	$90.50	$90.50
7 purchase totals =	$492.07		$528.1276	$528.13	$528.15	$528.20