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	$82.25	6.870%	$87.9006	$87.90	$87.90	$87.90
Purchase #2	$127.40	8.622%	$138.3844	$138.38	$138.40	$138.40
Purchase #3	$37.90	10.323%	$41.8124	$41.81	$41.80	$41.80
Purchase #4	$100.83	11.497%	$112.4224	$112.42	$112.40	$112.40
Purchase #5	$190.85	13.504%	$216.6224	$216.62	$216.60	$216.60
Purchase #6	$222.26	5.688%	$234.9021	$234.90	$234.90	$234.90
Purchase #7	$18.65	4.599%	$19.5077	$19.51	$19.50	$19.50
7 purchase totals =	$780.14		$851.5520	$851.54	$851.50	$851.50