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	$29.46	12.294%	$33.0818	$33.08	$33.10	$33.10
Purchase #2	$144.83	4.858%	$151.8658	$151.87	$151.85	$151.90
Purchase #3	$32.97	13.774%	$37.5113	$37.51	$37.50	$37.50
Purchase #4	$124.58	8.288%	$134.9052	$134.91	$134.90	$134.90
Purchase #5	$193.51	10.252%	$213.3486	$213.35	$213.35	$213.30
Purchase #6	$54.96	3.206%	$56.722	$56.72	$56.70	$56.70
Purchase #7	$239.37	7.810%	$258.0648	$258.06	$258.05	$258.10
7 purchase totals =	$819.68		$885.4995	$885.50	$885.45	$885.50