没具体完善
Private Sub Form_Load()
MsgBox CustIt(13.1234, 2)
End Sub
Public Function CustIt(a As Single, b As Integer) As Single
Dim abc() As String
Dim rightA As String
abc = Split(a, ".")
CustIt = abc(0) & "." & CStr(CInt(Left(abc(1), b)) + 1)
End Function