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	$52.49	12.555%	$59.0801	$59.08	$59.10	$59.10
Purchase #2	$192.83	7.189%	$206.6925	$206.69	$206.70	$206.70
Purchase #3	$123.30	8.756%	$134.0961	$134.10	$134.10	$134.10
Purchase #4	$117.71	4.384%	$122.8704	$122.87	$122.85	$122.90
Purchase #5	$103.60	7.510%	$111.3804	$111.38	$111.40	$111.40
Purchase #6	$23.27	12.583%	$26.1981	$26.20	$26.20	$26.20
Purchase #7	$90.88	8.333%	$98.453	$98.45	$98.45	$98.50
7 purchase totals =	$704.08		$758.7706	$758.77	$758.80	$758.90