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	$236.49	9.761%	$259.5738	$259.57	$259.55	$259.60
Purchase #2	$165.62	4.735%	$173.4621	$173.46	$173.45	$173.50
Purchase #3	$132.78	11.633%	$148.2263	$148.23	$148.25	$148.20
Purchase #4	$71.42	9.828%	$78.4392	$78.44	$78.45	$78.40
Purchase #5	$8.79	10.403%	$9.7044	$9.70	$9.70	$9.70
Purchase #6	$116.66	12.794%	$131.5855	$131.59	$131.60	$131.60
Purchase #7	$158.67	6.436%	$168.882	$168.88	$168.90	$168.90
7 purchase totals =	$890.43		$969.8733	$969.87	$969.90	$969.90