Once you have found a true pitch on one string (either from a tuning fork, pitch pipe, fixed pitch instrument such as a keyboard or - for you honky tonk heroes - the jukebox), the note at the 5th fret should match the note on the next highest string open; the note at the 7th fret should match the next lowest string open.
So, if you have your A (5th) string tuned to pitch (440), and if your guitar is set up correctly, the note at the 5th fret on the A (5th) string is a true D (open 4th string) and the 7th fret is a true E (open 6th string).
This works until you want to tune the B (2nd) string. The fourth fret on the G(3rd) string is your B (open 2nd string); The 8th fret on the B (2nd) string is your G (open 3rd string).
I find that I hear the tones better if I use harmonics. Play the harmonic at the 5th fret; this should match the harmonic on the 7th fret on the next highest string; again, it changes for the B.
I also check my tuning by playing a note on an open string and the same note at the 2nd fret two strings higher (or 3rd fret, on the B string). The 2nd fret on the D (4th) string matches the E (open 6th), the 2nd on the G (3rd) matches the A (open 5th), etc.
Ear training is a great idea, but there is no shame in using the box, particularly when you can't find a quiet place to tune.
Apologies, in advance, if I mis-stated anything here. I wanted to see if I could explain it, without having access to a guitar. I think it's right, but . . .