bathroom tiles

I want to hang a toilet-roll holder in my newly built bathroom and I'll have to drill through tiles. I'll be drilling about 6 inches from the side of the cistern and, on the other side, about 6 inches from the screen of a walk-in shower. Can I assume that bit of the wall will be clear of...

Firstly, before you flame me, I know this is not ideal but hear me out... I'm trying to put a bathroom together for a relatively low cost, it needs to do 1 year, maybe 2. It seems a little wasteful as it is, so I'm really trying to keep the costs down and can't contemplate getting a plasterer...