We present a 3D multiscale coupling method to address sliding contact simulations at the nanoscale. The components of the model are a molecular dynamics engine, a finite element program and a coupling scheme. We consider the normal loading of a rough (fractal) surface and discuss the influence of dislocation interactions beneath contacting asperities on the contact response. We then conduct a sliding simulation between two rough surfaces, which yields a direct prediction of the evolution of contact clusters.