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	$50.99	11.233%	$56.7177	$56.72	$56.70	$56.70
Purchase #2	$208.27	5.431%	$219.5811	$219.58	$219.60	$219.60
Purchase #3	$83.52	10.733%	$92.4842	$92.48	$92.50	$92.50
Purchase #4	$30.66	6.539%	$32.6649	$32.66	$32.65	$32.70
Purchase #5	$48.81	7.757%	$52.5962	$52.60	$52.60	$52.60
Purchase #6	$100.35	4.246%	$104.6109	$104.61	$104.60	$104.60
Purchase #7	$112.44	3.116%	$115.9436	$115.94	$115.95	$115.90
7 purchase totals =	$635.04		$674.5986	$674.59	$674.60	$674.60