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	$20.67	10.184%	$22.775	$22.78	$22.80	$22.80
Purchase #2	$221.72	13.162%	$250.9028	$250.90	$250.90	$250.90
Purchase #3	$17.95	12.106%	$20.123	$20.12	$20.10	$20.10
Purchase #4	$145.45	4.259%	$151.6447	$151.64	$151.65	$151.60
Purchase #5	$44.90	12.256%	$50.4029	$50.40	$50.40	$50.40
Purchase #6	$231.70	6.574%	$246.932	$246.93	$246.95	$246.90
Purchase #7	$44.93	3.752%	$46.6158	$46.62	$46.60	$46.60
7 purchase totals =	$727.32		$789.3962	$789.39	$789.40	$789.30