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	$111.42	5.715%	$117.7877	$117.79	$117.80	$117.80
Purchase #2	$34.79	8.861%	$37.8727	$37.87	$37.85	$37.90
Purchase #3	$109.39	13.176%	$123.8032	$123.80	$123.80	$123.80
Purchase #4	$235.39	10.763%	$260.725	$260.73	$260.75	$260.70
Purchase #5	$129.31	10.737%	$143.194	$143.19	$143.20	$143.20
Purchase #6	$127.52	13.381%	$144.5835	$144.58	$144.60	$144.60
Purchase #7	$32.62	13.861%	$37.1415	$37.14	$37.15	$37.10
7 purchase totals =	$780.44		$865.1076	$865.10	$865.15	$865.10