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	$80.61	3.182%	$83.175	$83.18	$83.20	$83.20
Purchase #2	$70.88	10.391%	$78.2451	$78.25	$78.25	$78.20
Purchase #3	$139.61	4.466%	$145.845	$145.85	$145.85	$145.80
Purchase #4	$46.56	13.628%	$52.9052	$52.91	$52.90	$52.90
Purchase #5	$219.56	12.730%	$247.51	$247.51	$247.50	$247.50
Purchase #6	$11.97	13.739%	$13.6146	$13.61	$13.60	$13.60
Purchase #7	$158.56	11.730%	$177.1591	$177.16	$177.15	$177.20
7 purchase totals =	$727.75		$798.4540	$798.47	$798.45	$798.40