The ordering of physically adsorbed gases on quasicrystalline surfaces exemplifies the effects of competing interactions. In this study, grand canonical Monte Carlo simulations were performed to complement experimental measurements of the ordering of Xe adsorbed on the tenfold surface of decagonal Al-Ni-Co. The simulations employed a semi-empirical gas-surface interaction, based on conventional combining rules, and the Lennard-Jones Xe-Xe interaction. The simulation results are consistent with the experiment and provide a new insight into the ordering behavior. The film initially has a fivefold quasicrystalline symmetry, but it evolves into a close-packed structure during adsorption of the second layer. The presence of symmetry defects in the sixfold structure creates domains of Xe having different (but equivalent) rotational epitaxy, suggesting that even in the absence of substrate defects, the annealed film has the five different rotational alignments observed in the experimental studies.