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	$75.62	3.756%	$78.4603	$78.46	$78.45	$78.50
Purchase #2	$111.49	4.565%	$116.5795	$116.58	$116.60	$116.60
Purchase #3	$26.87	11.118%	$29.8574	$29.86	$29.85	$29.90
Purchase #4	$18.52	10.446%	$20.4546	$20.45	$20.45	$20.50
Purchase #5	$216.99	13.445%	$246.1643	$246.16	$246.15	$246.20
Purchase #6	$248.42	11.749%	$277.6069	$277.61	$277.60	$277.60
Purchase #7	$167.46	9.172%	$182.8194	$182.82	$182.80	$182.80
7 purchase totals =	$865.37		$951.9424	$951.94	$951.90	$952.10