Rigorous approximation of stationary measures and convergence to equilibrium for iterated function systems *All the authors were partially supported by ICTP and by EU Marie-Curie IRSES Brazilian–European partnership in Dynamical Systems (FP7-PEOPLE-2012-IRSES 318999 BREUDS), SG thanks The Leverhulme Trust for support through Network Grant IN-2014-021. (27th May 2016)