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	$154.89	9.837%	$170.1265	$170.13	$170.15	$170.10
Purchase #2	$210.38	12.573%	$236.8311	$236.83	$236.85	$236.80
Purchase #3	$119.82	10.105%	$131.9278	$131.93	$131.95	$131.90
Purchase #4	$66.72	4.627%	$69.8071	$69.81	$69.80	$69.80
Purchase #5	$46.49	11.720%	$51.9386	$51.94	$51.95	$51.90
Purchase #6	$65.97	10.398%	$72.8296	$72.83	$72.85	$72.80
Purchase #7	$247.64	13.300%	$280.5761	$280.58	$280.60	$280.60
7 purchase totals =	$911.91		$1,014.0368	$1,014.05	$1,014.15	$1,013.90