Stannous Nitrate is obtained in white leaflets having the
composition $\ce{Sn(NO3)2.20H2O}$ by cooling to $\pu{-20 °C}$. a solution of
stannous oxide in nitric acid of density 1.2. It is also formed by the
action of highly diluted nitric acid on the metal, some of the acid
thus suffering maximum reduction to ammonia:
$$\ce{4Sn + 10HNO3 -> 4Sn(NO3)2 + NH4NO3 + 3H2O}$$
According to C. H. H. Walker, tin dissolves in nitric acid forming
stannous and stannic nitrates, the relative proportion of these two
salts produced depending on the temperature and the strength of the
acid; moreover, the yellowish white precipitate which separates when
the somewhat concentrated acid is employed is said to be a hydrated,
ill-defined, stannic nitrate.
Ref.: http://tin.atomistry.com/stannous_nitrate.html
You can also check the post linked by Ivan.