Note that at least in some tar implementations the order of options is meaningful when extracting files from an archive, you need to put the options like this:

tar -xvf <filename_of_archive.tar> --numeric-owner -C <target_directory>

The "sync" command makes sure that all file buffers are written to the device. It is pretty good to use especially after unpacking a load of files to make sure the changes really go to the file system.
On the other hand, I do believe that properly unmounting the FS should achieve the same result.