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	$233.54	9.265%	$255.1775	$255.18	$255.20	$255.20
Purchase #2	$144.43	3.653%	$149.706	$149.71	$149.70	$149.70
Purchase #3	$190.98	4.170%	$198.9439	$198.94	$198.95	$198.90
Purchase #4	$77.37	13.667%	$87.9442	$87.94	$87.95	$87.90
Purchase #5	$163.69	13.548%	$185.8667	$185.87	$185.85	$185.90
Purchase #6	$35.54	5.861%	$37.623	$37.62	$37.60	$37.60
Purchase #7	$46.86	11.386%	$52.1955	$52.20	$52.20	$52.20
7 purchase totals =	$892.41		$967.4568	$967.46	$967.45	$967.40