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	$54.72	12.238%	$61.4166	$61.42	$61.40	$61.40
Purchase #2	$184.54	11.357%	$205.4982	$205.50	$205.50	$205.50
Purchase #3	$7.83	12.550%	$8.8127	$8.81	$8.80	$8.80
Purchase #4	$20.58	5.513%	$21.7146	$21.71	$21.70	$21.70
Purchase #5	$104.35	13.531%	$118.4696	$118.47	$118.45	$118.50
Purchase #6	$34.51	10.103%	$37.9965	$38.00	$38.00	$38.00
Purchase #7	$171.59	12.425%	$192.9101	$192.91	$192.90	$192.90
7 purchase totals =	$578.12		$646.8183	$646.82	$646.75	$646.80