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	$59.79	6.760%	$63.8318	$63.83	$63.85	$63.80
Purchase #2	$21.65	12.782%	$24.4173	$24.42	$24.40	$24.40
Purchase #3	$175.72	7.738%	$189.3172	$189.32	$189.30	$189.30
Purchase #4	$132.27	3.793%	$137.287	$137.29	$137.30	$137.30
Purchase #5	$216.94	6.698%	$231.4706	$231.47	$231.45	$231.50
Purchase #6	$113.66	7.631%	$122.3334	$122.33	$122.35	$122.30
Purchase #7	$90.43	10.795%	$100.1919	$100.19	$100.20	$100.20
7 purchase totals =	$810.46		$868.8492	$868.85	$868.85	$868.80