Charge-state distributions and energy losses of 0.67--1.5-MeV He ions scattered from a clean (100) surface of a SnTe single crystal are studied at glancing-angle incidence under UHV conditions. A stochastic model of charge exchange and energy loss of ions is developed, where inelastic interactions depend on the distance of the ion from the surface. Observed charge-state fractions and energy losses of the reflected He ions are explained with the model. Taking account of scattering of ions at surface steps, which causes the deflection of ion trajectories, position-dependent charge-exchange probabilities of He ions near the surface are derived from the observed charge-state distributions and charge-state dependence of the energy losses of scattered He ions.