At TeV energies and above gamma rays can induce electromagnetic cascades, whose charged component is sensitive to intervening intergalactic magnetic fields (IGMFs). When interpreting gamma-ray measurements in the energy range between a few GeV and hundreds of TeV, one has to carefully account for effects due to IGMFs, which depend on their strength and power spectrum. Therefore, gamma-ray-induced electromagnetic cascades can be used as probes of cosmic magnetism, since their arrival distribution as well as spectral and temporal properties can provide unique information about IGMFs, whose origin and properties are currently poorly understood. In this contribution we present an efficient three-dimensional Monte Carlo code for simulations of gamma-ray propagation. We focus on the effects of different configurations of IGMFs, in particular magnetic helicity and the power spectrum of stochastic fields, on the morphology of the arrival directions of gamma rays, and discuss the prospects for detecting pair haloes around distant blazars.