type
  TTaxValues = class(TStringList)
  private
    const DEFAULT_TAX_VALUES = '18,10,18/118,10/110,0';
  public
    procedure AfterConstruction; overide;

	function IDOfTax(const ATaxValue: string): Integer;
  end;

procedure TTaxValues.AfterConstruction;
begin
  inherited;
  CommaText := DEFAULT_TAX_VALUES;
end;

function TTaxValues.IDOfTax(const ATaxValue: string): Integer;
begin
  Result := IndexOf(ATaxValue);
end
..