This paper addresses the problem of output voltage regulation at the point of common coupling (PCC) for multiple single-phase DC/AC inverters connected to a microgrid in islanded mode, and prescribes a robust decentralized scheme for sharing power among different sources. The problem of regulating voltage at PCC is posed as a disturbance-rejection problem, where the load current is regarded as an unknown disturbance signal and thus no assumptions are made regarding the power demanded by the load at the PCC. The disturbance-rejection controller has an inner-outer cascaded structure, where inner-current controller is parameterized by coupling inductance of the inverter, and is such that the inner-loop seen by the outer-voltage controller is identical for all the parallel inverters. This favors scalability by allowing multiple inverters to be added to the PCC without the need to separately design outer-loop controllers for individual inverters. A significant feature of the proposed control architecture is that the stability and performance analysis of the multi-inverter network is tractable; in fact, analysis can be done in terms of an equivalent single-inverter system. Case studies presented in this paper demonstrate the effectiveness of the proposed design in terms of voltage regulation, power sharing and robustness to parametric and modeling uncertainties.