Here is example with DOMDocument. I think this is the best solution in this case.
Code
For Each ElementCategory In DOMDocument.DocumentElement.ChildNodes Do
Message(ElementCategory.GetAttribute("DESCRIPTION"));
Message(ElementCategory.GetAttribute("CODE"));
ElementsGRUP = ElementCategory.GetElementByTagName("GRUP");
For Each ElementGRUP In ElementsGRUP Do
Message(ElementGRUP.GetAttribute("DESCRIPTION"));
Message(ElementGRUP.GetAttribute("CODE"));
For Each ElementProduct In ElementGRUP.GetElementByTagName("PRODUCT") Do
Message(ElementProduct.GetAttribute("PRODUCTNAME"));
Message(ElementProduct.GetElementByTagName("TAX")[0].TextContent);
EndDo;
EndDo;
EndDo;