How to get sales tax and Purch tax percentage in AX 2012

private TaxValue getTaxPercent(TaxGroup _taxGroup, TaxItemGroup _taxItemGroup)
{
    TaxGroupData    taxGroupData ;
    TaxOnItem       taxOnItem;
    TaxData         taxData;

    select firstonly TaxCode from taxGroupData
        index hint TaxGroupIdx
            where taxGroupData.TaxGroup == _taxGroup
            join taxOnItem
            where taxOnItem.TaxItemGroup == _taxItemGroup &&
                    taxOnItem.TaxCode == taxGroupData.TaxCode;

    select firstonly TaxValue from taxData where taxData.TaxCode == taxGroupData.TaxCode;
    return taxData.TaxValue;

}