how to keep adding the values when checkbox is checked?

When i check all the checkboxes the total still ends up being 10. I don't know what is going on here please help

Dim top As Integer
    Select Case top
        Case CheckBox1.Checked
            top = +10
        Case CheckBox2.Checked
            top = +10
        Case CheckBox3.Checked
            top = +10
        Case CheckBox4.Checked
            top = +10
        Case CheckBox5.Checked
            top = +10
        Case CheckBox6.Checked
            top = +10
    End Select
    TextBox2.Text = top