  We examine the tunneling spectroscopy of three-dimensional
normal-metal/Sr$_2$RuO$_4$ junctions as an experimental means to identify
pairing symmetry in Sr$_2$RuO$_4$. In particular, we consider three different
possible pairing states in Sr$_2$RuO$_4$: spin-singlet chiral $d$-wave,
spin-triplet helical $p$-wave, and spin-nematic $f$-wave ones, all of which are
consistent with recent nuclear-magnetic-resonance experiments [A. Pustogow et
al., Nature 574, 72 (2019)]. The Blonder-Tinkham-Klapwijk theory is employed to
calculate the tunneling conductance, and the cylindrical two-dimensional Fermi
surface of Sr$_2$RuO$_4$ is properly taken into account as an anisotropic
effective mass and a cutoff in the momentum integration. It is pointed out that
the chiral $d$-wave pairing state is inconsistent with previous tunneling
conductance experiments along the $c$-axis. We also find that the remaining
candidates, the spin-triplet helical $p$-wave pairing state and the
spin-nematic $f$-wave ones, can be distinguished from each other by the
in-plane tunneling spectroscopy along the $a$- and $b$-axes.

Superconductivity