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	$130.28	10.590%	$144.0767	$144.08	$144.10	$144.10
Purchase #2	$197.26	4.374%	$205.8882	$205.89	$205.90	$205.90
Purchase #3	$126.50	12.792%	$142.6819	$142.68	$142.70	$142.70
Purchase #4	$33.38	4.434%	$34.8601	$34.86	$34.85	$34.90
Purchase #5	$169.72	13.131%	$192.0059	$192.01	$192.00	$192.00
Purchase #6	$145.38	4.411%	$151.7927	$151.79	$151.80	$151.80
Purchase #7	$108.37	3.451%	$112.1098	$112.11	$112.10	$112.10
7 purchase totals =	$910.89		$983.4153	$983.42	$983.45	$983.50