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	$204.26	13.495%	$231.8249	$231.82	$231.80	$231.80
Purchase #2	$241.30	10.554%	$266.7668	$266.77	$266.75	$266.80
Purchase #3	$145.77	9.553%	$159.6954	$159.70	$159.70	$159.70
Purchase #4	$28.45	11.178%	$31.6301	$31.63	$31.65	$31.60
Purchase #5	$217.60	13.280%	$246.4973	$246.50	$246.50	$246.50
Purchase #6	$70.88	10.374%	$78.2331	$78.23	$78.25	$78.20
Purchase #7	$44.42	5.396%	$46.8169	$46.82	$46.80	$46.80
7 purchase totals =	$952.68		$1,061.4645	$1,061.47	$1,061.45	$1,061.40