  We perform a detailed comparison of magnetotunneling in conventional
low-$T_c$ Nb/AlAlOx/Nb junctions with that in slightly overdoped
Bi$_{2-y}$Pb$_y$Sr$_2$CaCu$_2$O$_{8+\delta}$ [Bi(Pb)-2212] intrinsic Josephson
junctions and with microscopic calculations. It is found that both types of
junctions behave in a qualitatively similar way. Both magnetic field and
temperature suppress superconductivity in the state-conserving manner. This
leads to the characteristic sign-change of tunneling magnetoresistance from the
negative at the sub-gap to the positive at the sum-gap bias. We derived
theoretically and verified experimentally scaling laws of magnetotunneling
characteristics and employ them for accurate extraction of the upper critical
field $H_{c2}$. For Nb an extended region of surface superconductivity at
$H_{c2}<H<H_{c3}$ is observed. The parameters of Bi(Pb)-2212 were obtained from
self-consistent analysis of magnetotunneling data at different levels of bias,
dissipation powers and for different mesa sizes, which precludes the influence
of self-heating. It is found that $H_{c2}(0)$ for Bi(Pb)-2212 is $\simeq 70$ T
and decreases significantly at $T\rightarrow T_c$. The amplitude of sub-gap
magnetoresistance is suppressed exponentially at $T>T_c/2$, but remains
negative, although very small, above $T_c$. This may indicate existence of an
extended fluctuation region, which, however, does not destroy the general
second-order type of the phase transition at $T_c$.
