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	$132.66	8.491%	$143.9242	$143.92	$143.90	$143.90
Purchase #2	$15.88	7.549%	$17.0788	$17.08	$17.10	$17.10
Purchase #3	$20.87	9.771%	$22.9092	$22.91	$22.90	$22.90
Purchase #4	$150.54	4.570%	$157.4197	$157.42	$157.40	$157.40
Purchase #5	$116.41	10.535%	$128.6738	$128.67	$128.65	$128.70
Purchase #6	$171.49	8.180%	$185.5179	$185.52	$185.50	$185.50
Purchase #7	$10.64	3.195%	$10.9799	$10.98	$11.00	$11.00
7 purchase totals =	$618.49		$666.5035	$666.50	$666.45	$666.50