  Nitrogen-bearing complex organic molecules have been commonly detected in the
gas phase but not yet in interstellar ices. This has led to the long-standing
question of whether these molecules form in the gas phase or in ices.
$\textit{James Webb}$ Space Telescope ($\textit{JWST}$) offers the sensitivity,
spectral resolution, and wavelength coverage needed to detect them in ices and
investigate whether their abundance ratios are similar in gas and ice. We
report the first tentative detection of CH$_3$CN, C$_2$H$_5$CN, and the simple
molecule, N$_2$O, based on the CN-stretch band in interstellar ices toward
three (HOPS 153, HOPS 370, and IRAS 20126+4104) out of the five protostellar
systems observed as part of the Investigating Protostellar Accretion (IPA) GO
program with $\textit{JWST}$-NIRSpec. We also provide upper limits for the two
other sources with smaller luminosities in the sample. We detect OCN$^-$ in the
ices of all sources with typical CH$_3$CN/OCN$^-$ ratios of around 1. Ice and
gas column density ratios of the nitrogen-bearing species with respect to each
other are better matched than those with respect to methanol, which are a
factor of ${\sim}5$ larger in the ices than the gas. We attribute the elevated
ice column densities with respect to methanol to the difference in snowline
locations of nitrogen-bearing molecules and of methanol, biasing the gas-phase
observations toward fewer nitrogen-bearing molecules. Moreover, we find
tentative evidence for enhancement of OCN$^-$, CH$_3$CN, and C$_2$H$_5$CN in
warmer ices, although formation of these molecules likely starts along with
methanol in the cold prestellar phase. Future surveys combining NIRSpec and
MIRI, and additional laboratory spectroscopic measurements of C$_2$H$_5$CN ice,
are necessary for robust detection and conclusions on the formation history of
complex cyanides.
