A slightly complicated but successful method is to use arrays and functions to call the sounds/songs instead of using the standard audio expressions.
This way you can control all sounds and music separately, and get rid of that awful clicking sounds that can still be heard when all audio should be muted. I can recommend checking out Advanced Menu in the Scirra Store - this includes a very effective menu select, settings like audio and language select, and achievements/trophies.
If you purely just wanted audio, create an array that can toggle between 2 values on sound on/off button. Then use a similar code like this as the function that will be called.
+ Function: On "PlaySound"
+ AOption: Value at 2 = "on"
-> Audio: Play Function.Param(0) not looping from Sounds at int(AOption.At(3)) dB (tag "")
Then, to call the sound, ie a menu click or a bullet firing, instead of using
-> Audio: Play bang_01.webm not looping at volume 0 dB (tag "") use the call function like this
-> Function: Call "PlaySound" ("bang_01")