You need to bring the Archive::Tar constructor out of the loop and after adding to the archive, you need to write the archive.

  my $tar = Archive::Tar->new;
  foreach $file (@files) {
    print $file;
    $tar->add_files(@files);
  }
  $tar->write( "foo.tar" );
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Doh! no need for a loop at all

  my $tar = Archive::Tar->new;
  $tar->add_files( @files );
  $tar->write( "foo.tar" );
[download]