There are numerous fade options in recent releases.
Set your video fade.
Right-click the audio track and click Fade Out. Click the From End of the Clip button, then set the same duration as video.
The timeline waveform line should confirm that the lengths are the same. 
If A/V don't correspond, try reinserting the clip on the timeline, then applying the fades. Or use another of the right-click audio menu options.