Equal probability values from non-normal distribution

Hello gentlemen,

I am a beginner in Matlab, so my question might seem as kind of a "blond question". I have generated values from a "PERT" distribution ( it is kind of a non-normal distribution) and I am trying to find values, which. - are located around the mode - have equal probabilities - contain 10% (20,30,40,50... etc) volume of the distribution mass.

Any ideas what specific function I can use? Any help will be highly appreciated.

Thanks in advance