https://dor.wa.gov/find-taxes-rates/retail-sales-tax/destination-based-sales-tax-and-streamlined-sales-tax/wa-sales-tax-rate-lookup-url-interface

WA Sales Tax Rate Lookup MODX Snippet

<?php
$output = '';

function isValidZipCode($zipCode) {
    return (preg_match('/^[0-9]{5}(-[0-9]{4})?$/', $zipCode)) ? true : false;
}

//$format  = !empty($format)      ? '?output='.urlencode(trim($format)) : '?output=text';
$address = !empty($address)       ? '&addr='.urlencode(trim($address))  : '&addr=';
$city    = !empty($city)          ? '&city='.urlencode(trim($city))     : '&city=';
$zip2     = isValidZipCode($zip)  ? '&zip='.$zip                        : '';
$url = 'https://webgis.dor.wa.gov/webapi/AddressRates.aspx?output=xml'.$address.$city.$zip2;

if ($zip2 !== '' && $zip2 !== '&zip=') {
    if (curl_init() === false) {
       $modx->log(modX::LOG_LEVEL_ERROR, 'Curl init failed');
    } else {
        $curl = curl_init();
        curl_setopt_array($curl, array(
            CURLOPT_URL => $url,
            CURLOPT_HTTPHEADER => array('Content-Type: text/xml'),
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_HTTPGET => true
        ));
        $data = curl_exec($curl);
        if(!curl_exec($curl)){
            $modx->log(modX::LOG_LEVEL_ERROR, curl_error($curl));
        } 
        curl_close($curl);
    
        $xml = simplexml_load_string($data, 'SimpleXMLElement', LIBXML_NOCDATA);
        if ((int)$xml->attributes()->code->__toString() <= 5){
            // http://php.net/manual/en/simplexmlelement.attributes.php
            $rate = $xml->attributes()->rate->__toString();
            $loccode = $xml->attributes()->loccode->__toString();
            $localrate = $xml->attributes()->localrate->__toString();
            $staterate = $xml->rate["staterate"]->__toString();
            $name = $xml->rate["name"]->__toString();
            $period = $xml->addressline["period"]->__toString();
            $ptba = $xml->addressline["ptba"]->__toString();
    
            $output = '<span data-toggle="tooltip" title="DOR: ' . $loccode . ', Local Rate: ' . $localrate . ', State Rate: ' . $staterate . ', Combined: ' . $rate . ', PTBA: ' . $ptba . ', TAX PERIOD: ' . $period . '">' .$name .' WA: <b>' . ($rate*100) . '%</b></span><br>';
        } else {
            $output = '<a data-toggle="modal" style="cursor:pointer" data-remote="[[~43]]" data-target="#taxMap">&raquo; State Tax Rates</a>';
        }
    }
} else {
    $output = '<a data-toggle="modal" style="cursor:pointer" data-remote="[[~43]]" data-target="#taxMap">&raquo; State Tax Rates</a>';
}
return $output;