Python3 ImportError: No module named '_tkinter'

I think you still need to install the tkinker package. You can do this by simply typing:

sudo apt-get install python3-tk

The issue as I see is that you are still calling your python3.5 binaries which might be set as default python interface. See the line in your error which tells the version of python it is referring to:

/usr/local/lib/python3.5/tkinter/

If it's a UNIX / Linux flavour you are using, you can check where are your python binaries by using

whereis python

and you will get a list of all the flavours and places it is in:

You simply call out your chosen flavor to work with, which I am guessing might be

/usr/local/bin/python3.6

and then list the available modules to check if Tkinter is available or not, although it is highly unlikely not to as it comes bundled as a standard library.