Command block inaccurate when using the tp command

When using a command block, I used the tp command to teleport the nearest player to a coordinate. The command block teleported the player to a coordinate that was inaccurate, the x and y had changed.
There was a water block in the coordinate that I wanted, but I changed it afterwards and it still wouldn't. It was directly above the command block and so would have resulted in a loop of teleporting, and I don't know if the command blocks are programmed to change the coordinate if that is the case.

Screenshots are attached.