How to install 2x10 joists of slightly different sizes?
Use face mount joist hangers and set them so that the tops of the joists are all level.

You could try to return the joists and demand a batch that are the same size. Or shim them, which is less than ideal.

As stated in comments, joists can vary in size based on moisture content. Not only that, but they'll expand and contract a bit with moisture changes in the future, as well.