I think this is the best one: Converting between XML and JSON

Be sure to read the accompanying article on the xml.com O'Reilly site, which goes into details of the problems with these conversions, which I think you will find enlightening. The fact that O'Reilly is hosting the article should indicate that Stefan's solution has merit.

You can use http://goessner.net/download/prj/jsonxml/ like this using the function json2xml:

var data = '{"Data":{"SOM":{"Tab":[{"Values":{"SelectedValues":null,"LoadedValues":null,"ExpandedValues":null,"ID":"msorgrole"},"ID":"OrgRole"},{"Values":{"SelectedValues":null,"LoadedValues":null,"ExpandedValues":null,"ID":"msorg"},"ID":"Organization"},{"Values":{"SelectedValues":null,"LoadedValues":null,"ExpandedValues":null,"ID":"mscontenttype"},"ID":"PeopleType"},{"Values":{"SelectedValues":",B79720D5-0E95-4CB7-B4F9-37BE24696F4F,831A2A77-B758-493A-B0F4-991A6427C31C,","LoadedValues":null,"ExpandedValues":null,"ID":"mspeople"},"ID":"People"}]}}}';

var jsonObj = JSON.parse(data); // important to first convert json string into object

alert(json2xml(jsonObj));

<script src="http://goessner.net/download/prj/jsonxml/json2xml.js"></script>

replace your OBJtoXML function with

function OBJtoXML(obj) {
  var xml = '';
  for (var prop in obj) {
    xml += obj[prop] instanceof Array ? '' : "<" + prop + ">";
    if (obj[prop] instanceof Array) {
      for (var array in obj[prop]) {
        xml += "<" + prop + ">";
        xml += OBJtoXML(new Object(obj[prop][array]));
        xml += "</" + prop + ">";
      }
    } else if (typeof obj[prop] == "object") {
      xml += OBJtoXML(new Object(obj[prop]));
    } else {
      xml += obj[prop];
    }
    xml += obj[prop] instanceof Array ? '' : "</" + prop + ">";
  }
  var xml = xml.replace(/<\/?[0-9]{1,}>/g, '');
  return xml
}