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	$122.48	12.782%	$138.1354	$138.14	$138.15	$138.10
Purchase #2	$32.65	13.141%	$36.9405	$36.94	$36.95	$36.90
Purchase #3	$227.47	12.231%	$255.2919	$255.29	$255.30	$255.30
Purchase #4	$199.76	11.105%	$221.9433	$221.94	$221.95	$221.90
Purchase #5	$84.95	13.584%	$96.4896	$96.49	$96.50	$96.50
Purchase #6	$56.92	5.240%	$59.9026	$59.90	$59.90	$59.90
Purchase #7	$143.87	3.189%	$148.458	$148.46	$148.45	$148.50
7 purchase totals =	$868.10		$957.1613	$957.16	$957.20	$957.10