We investigate the low-field magnetotransport properties of a two-dimensional electron gas with a strong magnetic modulation in two directions by means of the classical Kubo theory. The magnetoresistivity shows distinct maxima, which do not correspond to pinned orbits commensurate with the superlattice constant in contrast to electrostatic antidot systems. The features in the magnetoresistivity can be ascribed to the interplay between the chaotic dynamics of the system and regular motion on open trajectories through the superlattice.