Transform a List<Map<String,String>> to a String ( xml formatted ) using grouping

gistfile1.txt

  
  
    Origin = List<HashMap<String,String>>
    [ [skuid=10, date_eff=JAN, date_inac=FEB, vat_code_att=S, pcnt_to_aply=80],
      [skuid=10, date_eff=JAN, date_inac=FEB, vat_code_att=Z, pcnt_to_aply=20],
      [skuid=10, date_eff=MAR, date_inac=APR, vat_code_att=S, pcnt_to_aply=100]
    ]
    
    Destination = String
    <SkuTax skuId="10">
      <SkuTaxPeriod date_eff="JAN" date_inac="FEB">
        <Tax vatCode="S" pcnt="80"/>
        <Tax vatCode="Z" pcnt="20"/>
      </SkuTaxPeriod>
      <SkuTaxPeriod date_eff="MAR" date_inac="APR">
        <Tax vatCode="S" pcnt="100"/>
      </SkuTaxPeriod>
    </SkuTax>
     */