function getXmlHttpRequest() {
    try {
        return new XMLHttpRequest(); // Firefox, Opera 8.0+, Safari
    } catch (e) { }
    try {
        return new ActiveXObject("Msxml2.XMLHTTP");
    } catch (e) { }
    try {
        return new ActiveXObject("Microsoft.XMLHTTP");
    }  catch (e) { }
    return null;
}

function updateTaxas() {
    var xmlHttp = getXmlHttpRequest();
    xmlHttp.open("POST", "http://www.bancoob.com.br/taxas/index.php", true);
    xmlHttp.onreadystatechange = function() {};
    xmlHttp.send(null);
}