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	$232.25	10.246%	$256.0463	$256.05	$256.05	$256.00
Purchase #2	$40.72	12.794%	$45.9297	$45.93	$45.95	$45.90
Purchase #3	$40.67	8.810%	$44.253	$44.25	$44.25	$44.30
Purchase #4	$68.72	11.720%	$76.774	$76.77	$76.75	$76.80
Purchase #5	$70.70	11.461%	$78.8029	$78.80	$78.80	$78.80
Purchase #6	$34.34	4.448%	$35.8674	$35.87	$35.85	$35.90
Purchase #7	$53.78	11.469%	$59.948	$59.95	$59.95	$59.90
7 purchase totals =	$541.18		$597.6213	$597.62	$597.60	$597.60