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	$38.42	5.451%	$40.5143	$40.51	$40.50	$40.50
Purchase #2	$226.38	13.151%	$256.1512	$256.15	$256.15	$256.20
Purchase #3	$133.81	4.201%	$139.4314	$139.43	$139.45	$139.40
Purchase #4	$103.49	13.618%	$117.5833	$117.58	$117.60	$117.60
Purchase #5	$12.93	13.822%	$14.7172	$14.72	$14.70	$14.70
Purchase #6	$136.39	5.837%	$144.3511	$144.35	$144.35	$144.40
Purchase #7	$239.48	7.380%	$257.1536	$257.15	$257.15	$257.20
7 purchase totals =	$890.90		$969.9021	$969.89	$969.90	$970.00