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	$74.72	5.173%	$78.5853	$78.59	$78.60	$78.60
Purchase #2	$125.70	9.664%	$137.8476	$137.85	$137.85	$137.80
Purchase #3	$218.43	10.593%	$241.5683	$241.57	$241.55	$241.60
Purchase #4	$120.67	5.656%	$127.4951	$127.50	$127.50	$127.50
Purchase #5	$145.41	11.825%	$162.6047	$162.60	$162.60	$162.60
Purchase #6	$66.90	8.516%	$72.5972	$72.60	$72.60	$72.60
Purchase #7	$123.40	6.509%	$131.4321	$131.43	$131.45	$131.40
7 purchase totals =	$875.23		$952.1303	$952.14	$952.15	$952.10