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	$140.33	10.324%	$154.8177	$154.82	$154.80	$154.80
Purchase #2	$13.66	9.795%	$14.998	$15.00	$15.00	$15.00
Purchase #3	$34.51	11.642%	$38.5277	$38.53	$38.55	$38.50
Purchase #4	$133.65	8.189%	$144.5946	$144.59	$144.60	$144.60
Purchase #5	$38.38	10.762%	$42.5105	$42.51	$42.50	$42.50
Purchase #6	$89.93	12.848%	$101.4842	$101.48	$101.50	$101.50
Purchase #7	$80.80	4.516%	$84.4489	$84.45	$84.45	$84.40
7 purchase totals =	$531.26		$581.3816	$581.38	$581.40	$581.30