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	$65.95	6.158%	$70.0112	$70.01	$70.00	$70.00
Purchase #2	$139.93	3.333%	$144.5939	$144.59	$144.60	$144.60
Purchase #3	$153.81	10.621%	$170.1462	$170.15	$170.15	$170.10
Purchase #4	$105.92	10.666%	$117.2174	$117.22	$117.20	$117.20
Purchase #5	$85.60	5.688%	$90.4689	$90.47	$90.45	$90.50
Purchase #6	$24.32	13.105%	$27.5071	$27.51	$27.50	$27.50
Purchase #7	$92.71	8.501%	$100.5913	$100.59	$100.60	$100.60
7 purchase totals =	$668.24		$720.5360	$720.54	$720.50	$720.50