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	$68.75	13.660%	$78.1413	$78.14	$78.15	$78.10
Purchase #2	$111.98	11.437%	$124.7872	$124.79	$124.80	$124.80
Purchase #3	$233.36	9.527%	$255.5922	$255.59	$255.60	$255.60
Purchase #4	$136.78	9.730%	$150.0887	$150.09	$150.10	$150.10
Purchase #5	$99.44	6.577%	$105.9802	$105.98	$106.00	$106.00
Purchase #6	$15.87	4.289%	$16.5507	$16.55	$16.55	$16.60
Purchase #7	$19.48	10.128%	$21.4529	$21.45	$21.45	$21.50
7 purchase totals =	$685.66		$752.5932	$752.59	$752.65	$752.70