It sounds like you may have accidentally enabled *[Snapping][1]*.

You can disable it by clicking the magnet icon in *3D view > Header*:

![enter image description here][2] ![enter image description here][3]


  [1]: http://wiki.blender.org/index.php/Doc:2.6/Manual/3D_interaction/Transform_Control/Snap_to_Mesh#Transform_Snapping
  [2]: https://i.sstatic.net/A6zFc.png
  [3]: https://i.sstatic.net/6re11.png