Owning tanks is a little different than owning the rest of your gear (which I'm all for.) For the amount of local diving you plan it may make more sense to rent. You might want to add up how much it will cost you to buy tanks, get them filled, annual VIP, hydro every 5 years. And compare against what it it would cost you to rent.
One reason to own tanks even if it doesn't pay is convienience. Just like you will usually dive more if you own the rest of your gear and don't have to mess with rentals or work around the hours of the shop, it is handy to have filled tanks at home waiting to go anytime. It's hard to say if picking up and returning rental tanks is actually any more trouble than getting your own filled though. Sometimes they will fill while you wait, and others you may have to drop off and pick up later so it's 2 trips anyway.
Another reason to own tanks would be because you would prefer a different type of tank than you can rent - perhaps you will find you can only rent AL80s, but would prefer to dive with steel 100s (for example.)