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	$219.75	7.239%	$235.6577	$235.66	$235.65	$235.70
Purchase #2	$75.47	10.682%	$83.5317	$83.53	$83.55	$83.50
Purchase #3	$77.95	9.670%	$85.4878	$85.49	$85.50	$85.50
Purchase #4	$80.45	12.538%	$90.5368	$90.54	$90.55	$90.50
Purchase #5	$20.43	5.674%	$21.5892	$21.59	$21.60	$21.60
Purchase #6	$45.57	5.684%	$48.1602	$48.16	$48.15	$48.20
Purchase #7	$70.77	5.477%	$74.6461	$74.65	$74.65	$74.60
7 purchase totals =	$590.39		$639.6095	$639.62	$639.65	$639.60