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	$23.45	4.616%	$24.5325	$24.53	$24.55	$24.50
Purchase #2	$241.71	12.180%	$271.1503	$271.15	$271.15	$271.20
Purchase #3	$78.71	8.105%	$85.0894	$85.09	$85.10	$85.10
Purchase #4	$200.54	10.508%	$221.6127	$221.61	$221.60	$221.60
Purchase #5	$18.78	8.156%	$20.3117	$20.31	$20.30	$20.30
Purchase #6	$136.86	11.759%	$152.9534	$152.95	$152.95	$153.00
Purchase #7	$229.43	12.246%	$257.526	$257.53	$257.55	$257.50
7 purchase totals =	$929.48		$1,033.1760	$1,033.17	$1,033.20	$1,033.20