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	$250.51	3.587%	$259.4958	$259.50	$259.50	$259.50
Purchase #2	$51.66	8.276%	$55.9354	$55.94	$55.95	$55.90
Purchase #3	$25.81	13.830%	$29.3795	$29.38	$29.40	$29.40
Purchase #4	$200.59	10.855%	$222.364	$222.36	$222.35	$222.40
Purchase #5	$142.87	5.401%	$150.5864	$150.59	$150.60	$150.60
Purchase #6	$42.34	3.456%	$43.8033	$43.80	$43.80	$43.80
Purchase #7	$220.69	4.611%	$230.866	$230.87	$230.85	$230.90
7 purchase totals =	$934.47		$992.4304	$992.44	$992.45	$992.50