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	$38.83	6.797%	$41.4693	$41.47	$41.45	$41.50
Purchase #2	$137.93	4.693%	$144.4031	$144.40	$144.40	$144.40
Purchase #3	$205.98	13.202%	$233.1735	$233.17	$233.15	$233.20
Purchase #4	$19.54	10.634%	$21.6179	$21.62	$21.60	$21.60
Purchase #5	$105.27	5.437%	$110.9935	$110.99	$111.00	$111.00
Purchase #6	$76.86	7.553%	$82.6652	$82.67	$82.65	$82.70
Purchase #7	$244.76	8.485%	$265.5279	$265.53	$265.55	$265.50
7 purchase totals =	$829.17		$899.8504	$899.85	$899.80	$899.90