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	$13.54	12.434%	$15.2236	$15.22	$15.20	$15.20
Purchase #2	$49.89	3.733%	$51.7524	$51.75	$51.75	$51.80
Purchase #3	$97.40	11.724%	$108.8192	$108.82	$108.80	$108.80
Purchase #4	$80.99	11.762%	$90.516	$90.52	$90.50	$90.50
Purchase #5	$124.33	9.799%	$136.5131	$136.51	$136.50	$136.50
Purchase #6	$233.53	5.249%	$245.788	$245.79	$245.80	$245.80
Purchase #7	$42.33	13.506%	$48.0471	$48.05	$48.05	$48.00
7 purchase totals =	$642.01		$696.6594	$696.66	$696.60	$696.60