The answer depends on what you listen on daily basis. If you listen 0dB sine waves during the daily commute, I see no problem with tuning using 0dB tones.
However, personally, I would use a test tone that's not louder than -5dB. Look at normal music, such as something instrumental or without too much synthetic bass. The peaks of bass SPL on such records are short lived and they reach about -10dB or less on well recorded CDs and perhaps -5dB on "loud tracks". In fact, for such music, -10dB test tone should be safe. After all, if the recording is "loud", you will not be listening it with the head unit volume knob position where it was normally for playing older CDs records that are not so loud. Moreover, even if peaks are at -5dB, they're short lived (in fact, this is why it's perfectly fine not to use DMM if you don't listen rap, dubstep, etc just level match sub with front speakers, and that's that). Now, rap or any music with much synthetic bass is different as the bass content can have long lasting peaks that can also be quite high. I don't have much rap in my collection. For the songs that I checked in foober2000 spectrum graph, the peaks of bass reach something like -5dB. So I really see why I should use a test tone louder than -5dB at all.