Textbox Round Down function

Well I've searched the forum a lot I have found plenty of round up formatting but none suits my perposes
I've got 2 radio buttons to select if i want roundup or rounddown but i don't manage to get the round down process to work.
Anyone who can help?

Private Sub txt_fpa_Change()
    Dim Temp As String
    Temp = WorksheetFunction.Substitute(txt_fpa.Text, ".", ",")
    txt_fpa.Value = Format(CDbl(Temp), "0.00")
    If txt_fpa.Value = "" Then
    exit sub
    Else
    txt_sum.Value = CDbl(txt_axia) + CDbl(txt_fpa)
    TextBox1.Value = Format(CDbl(txt_axia) + CDbl(txt_fpa), "0.00")
    'TextBox1.Value = Application.Round(CDbl(txt_axia) + (CDbl(txt_fpa.Value)), 2)
    End If

End Sub

Thank you in advance.