Python GUI with Checkboxes

I have been struggling with this problem over the past week and need some help. I am trying to write a GUI to calculate a total of all the checkboxes selected. Here is my code so far:

import tkinter
import tkinter.messagebox

class Joes_auto:

    def __init__(self):

        # Create the main window.
        self.main_window = tkinter.Tk()

        # Create the frames.  One for the checkbuttons,
        # one for the total frame, and one for the buttons
        self.top_frame = tkinter.Frame(self.main_window)
        self.mid_frame = tkinter.Frame(self.main_window)
        self.bottom_frame = tkinter.Frame(self.main_window)

        #Create the IntVar objects to use with the checkbuttons
        self.oil_change = tkinter.IntVar()
        self.lube_job = tkinter.IntVar()
        self.radiator_flush = tkinter.IntVar()
        self.transmission_flush = tkinter.IntVar()
        self.inspection = tkinter.IntVar()
        self.muffler_replacement = tkinter.IntVar()
        self.tire_rotation = tkinter.IntVar()

        # Set the IntVar objects to 0
        self.oil_change.set(0)
        self.lube_job.set(0)
        self.radiator_flush.set(0)
        self.transmission_flush.set(0)
        self.inspection.set(0)
        self.muffler_replacement.set(0)
        self.tire_rotation.set(0)

        # Create the Checkbutton widgets in the top_frame
        self.oil_change = tkinter.Checkbutton(self.top_frame, text = 'Oil Change ($30)', \
                                                variable=self.oil_change)
        self.lube_job = tkinter.Checkbutton(self.top_frame, text = 'Lube Job ($20)', \
                                            variable=self.lube_job)
        self.radiator_flush = tkinter.Checkbutton(self.top_frame, text = 'Radiator Flush ($40)', \
                                          variable=self.radiator_flush)
        self.transmission_flush = tkinter.Checkbutton(self.top_frame, text = 'Transmission Flush ($100)', \
                                              variable=self.transmission_flush)
        self.inspection = tkinter.Checkbutton(self.top_frame, text = 'Inspection ($35)', \
                                      variable=self.inspection)
        self.muffler_replacement = tkinter.Checkbutton(self.top_frame, text = 'Muffler Replacement ($200)', \
                                               variable=self.muffler_replacement)
        self.tire_rotation = tkinter.Checkbutton(self.top_frame, text = 'Tire Rotation ($20)', \
                                         variable=self.tire_rotation)

        # Pack the Checkbuttons
        self.oil_change.pack()
        self.lube_job.pack()
        self.radiator_flush.pack()
        self.transmission_flush.pack()
        self.inspection.pack()
        self.muffler_replacement.pack()
        self.tire_rotation.pack()

        # Create a total and quit button
        self.total_button = tkinter.Button(self.bottom_frame, text = 'Calculate Total', \
                                           command = self.total)
        self.quit_button = tkinter.Button(self.bottom_frame, text = 'Quit', \
                                           command = self.main_window.destroy)

        # Pack the buttons
        self.total_button.pack(side = 'left')
        self.quit_button.pack(side = 'left')

        # Pack the frames
        self.top_frame.pack()
        self.mid_frame.pack()
        self.bottom_frame.pack()

        # Start the mainloop
        tkinter.mainloop()

    def total(self):

        self.total = 0

        if self.oil_change.get() == 1:
            self.total += 30
        if self.lube_job.get() == 1:
            self.total += 20
        if self.radiator_flush.get() == 1:
            self.total += 40
        if self.transmission_flush.get() == 1:
            self.total += 100
        if self.inspection.get() == 1:
            self.total += 35
        if self.muffler_replacement.get() == 1:
            self.total += 200
        if self.tire_rotation.get() == 1:
            self.total += 20

        tkinter.messagebox.showinfo("Your total is", self.total)

joes_auto = Joes_auto()

Every time I run the program I get the AttributeError: Checkbutton has no attribute 'get'. I want the program to calculate the total of all the services checked and display the total.