The --verbose list from tar appears on *STDERR. There are lots of ways to get at it, but here is a tidy way with PerlIO, perl 5.8+

{
    open local(*STDERR), '>', \my $verbosity or die $!;
    my $status = system "/bin/tar -cv *.foo 1>$tarfile";
    # parse $verbosity and log it
}
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The use of a single string argument to system is not recommended, but for an archive/logging program that runs from cron there are few dangers. The single argument is desirable to invoke the shell to recognise output redirection and filename globbing.