Visual Basic.NET - redondeo de decimales

Dim tabla As New DataTable

Dim sql As String = "Select * FROM clientes Where Numcli = " + ComboBox1.SelectedValue.ToString + ""

Dim adp As New OleDbDataAdapter(sql, conectar)

adp.Fill(tabla)

For Each row As DataRow In tabla.Rows

    LblCuit.Text = row("cuit").ToString

    LblIva.Text = row("iva").ToString

    TxtLista.Text = row("NumLis")

    VarCod = row("NumCli")

    TxtCorredor.Text = row("NumCor")

    ''''''''''''''''''''''''''

    BtCancel.Enabled = True

    BtGrabarGral.Enabled = True

Next

Dim CMDTRA As String = "insert into AuxFacturacion (Cadena, Descripcion, FCantidad, P_Unitario, Importe )  values (@Cad, @Descrip,

@Can, @PUn, @Imp)"

Dim CMD As New OleDb.OleDbCommand(CMDTRA, conectar)

CMD.Parameters.AddWithValue("@Cad", row("Cadena"))

CMD.Parameters.AddWithValue("@Descrip", TxtDescrip.Text)

CMD.Parameters.AddWithValue("@Can", row("Ccantidad"))

CMD.Parameters.AddWithValue("@PUn", Val(TxtPU.Text))

CMD.Parameters.AddWithValue("@Imp", Val(TxtPU.Text) * row("Ccantidad"))

If ((CMD.ExecuteNonQuery() > 0)) Then

CMD.Parameters.AddWithValue("@PUn", CType(TxtPU.Text, Double))

CMD.Parameters.AddWithValue("@Imp", CType(TxtPU.Text, Double) )

textbox3.text = val(textbox1.text) + val(textbox2.text)

Textbox1.text= 120

Textbox2.text=20.25   (con punto)

Textbox1.text= 120

Textbox2.text=20,25   (con coma)