If they tip up on one end, or even stand upright, they're still ok to eat. It just means the egg has lost moisture, and the air cell is bigger. By the time they actually float like a cork, they're too old. If you aren't sure, you can always break them into a bowl, one at a time, when you're ready to use them. If an egg is bad enough to hurt you, it won't look normal when you break it open. It won't smell normal, either. You can see for sure whether they're ok before you dump them into the skillet or whatever you're cooking. 
In many years of doing this, I've never had a fresh egg float, but a fresh egg with little cracks in it will sometime tip up on one end. I use those anyway. (I wash all my eggs, so they all get water tested) I've had ONE bad egg not float. It wasn't actually spoiled, it didn't stink, but it was one my dog brought up to the house from who knows where. It sank, but wanted to only lay one way. If I rolled the other side up, it would slide right back over again. I broke it into a cup to see what was happening. The egg had apparently sat out in a sunny spot, (it was during VERY hot weather) the yolk looked partially cooked, and was stuck to the shell on that side. One of the weirdest things I've seen in an egg. Of course I threw that one out.