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	$80.49	12.546%	$90.5883	$90.59	$90.60	$90.60
Purchase #2	$19.54	11.456%	$21.7785	$21.78	$21.80	$21.80
Purchase #3	$201.64	6.544%	$214.8353	$214.84	$214.85	$214.80
Purchase #4	$210.25	12.528%	$236.5901	$236.59	$236.60	$236.60
Purchase #5	$52.97	3.491%	$54.8192	$54.82	$54.80	$54.80
Purchase #6	$155.31	9.497%	$170.0598	$170.06	$170.05	$170.10
Purchase #7	$177.72	5.304%	$187.1463	$187.15	$187.15	$187.10
7 purchase totals =	$897.92		$975.8175	$975.83	$975.85	$975.80