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	$143.67	10.779%	$159.1562	$159.16	$159.15	$159.20
Purchase #2	$225.47	13.226%	$255.2907	$255.29	$255.30	$255.30
Purchase #3	$16.48	5.464%	$17.3805	$17.38	$17.40	$17.40
Purchase #4	$97.78	5.854%	$103.504	$103.50	$103.50	$103.50
Purchase #5	$203.83	13.521%	$231.3899	$231.39	$231.40	$231.40
Purchase #6	$62.27	6.126%	$66.0847	$66.08	$66.10	$66.10
Purchase #7	$78.67	6.268%	$83.601	$83.60	$83.60	$83.60
7 purchase totals =	$828.17		$916.4070	$916.40	$916.45	$916.50