First it depends on the type of rock whether or not it will affect your pH etc.
Second it depends on where you found htema nd the likelihood that any pesticides or fertilizers etc would be on them, in which case NO.
Third boiling is a wonderful way to sterilize things, but... boiling certain types of rocks can cause them to explode. Much better to boil water then pour it over the rocks, and even then a face mask would be advisable. A rock chip going into your eye is not good.
SO in short, what kind of rock and where you found it is a good thing to think over. If there is a pesticide of any sort even boiling them (Which is dangerous) would not get all of it out, and could potentially kill the fish, and embed itself in any filter medium to lurk waiting to kill more.
With all that said, rocks that are suitable for tanks are a greeat thing, and benificial bacteria will colonize the porous ones to help your tank's biofilter immenously.
Wolfy