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	$46.31	6.302%	$49.2285	$49.23	$49.25	$49.20
Purchase #2	$129.46	12.103%	$145.1285	$145.13	$145.15	$145.10
Purchase #3	$123.67	13.106%	$139.8782	$139.88	$139.90	$139.90
Purchase #4	$171.47	11.323%	$190.8855	$190.89	$190.90	$190.90
Purchase #5	$95.29	13.197%	$107.8654	$107.87	$107.85	$107.90
Purchase #6	$228.78	10.571%	$252.9643	$252.96	$252.95	$253.00
Purchase #7	$65.49	8.746%	$71.2178	$71.22	$71.20	$71.20
7 purchase totals =	$860.47		$957.1682	$957.18	$957.20	$957.20