Q:

PHP Passing variables to a function and losing values

I am passing some variables to a function to round and add a dollars sign but when the values get into the function they have lost their values. 
formatDollars($cost, $taxedCost, $shipping, $total)

function formatDollars($cost, $taxedCost, $shipping, $total) {
    $taxedCost = '$'.round($taxedCost, 2);
    $shipping = '$'.round($shipping, 2);
    $total = '$'.round($total, 2);
    $cost = '$'.round($cost, 2);
    return array($cost, $taxedCost, $shipping, $total);
}

list($cost, $taxedCost, $shipping, $total) = formatDollars();

When I output I get the dollar signs but all my numbers have become zero. 

A:

I ended up finding the answer to my own quesion
In the line that I send variables to the function it did not like not having a variable to equal to, so when I ended up saying my variables equalled sending to the function. 
function formatDollars($numberFormatted)
    {
        $numberFormat = '$'.round($numberFormatted, 2);
        return $numberFormat;
    }
    $cost = formatDollars($cost);
    $taxedCost = formatDollars($taxedCost);
    $shipping = formatDollars($shipping);
    $total = formatDollars($total);

