  We present a numerically exact study of charge transport and its fluctuations
through a molecular junction driven out of equilibrium by a bias voltage, using
the Inchworm quantum Monte Carlo (iQMC) method. After showing how the technique
can be used to address any lead geometry, we concentrate on one dimensional
chains as an example. The finite bandwidth of the leads is shown to affect
transport properties in ways that cannot be fully captured by quantum master
equations: in particular, we reveal an interaction-induced broadening of
transport channels that is visible at all voltages, and show how fluctuations
of the current are a more sensitive probe of this effect than the mean current.
