An imaging system includes a roller assembly adapted to guide sheet material in the system into an accumulator and a sheet registration assembly. The registration assembly includes a lateral fence extending along a first edge of the accumulator. The lateral fence is adapted to contact a lateral edge of sheets fed into the accumulator. A longitudinal fence extends along a second edge of the accumulator. The longitudinal fence is adapted to contact a longitudinal edge of sheets fed into the accumulator. A fixed cam is included in the roller assembly. A rotatable registration finger is mounted in contact with the cam. During rotation of the registration finger, interaction between the registration finger and the cam causes the registration finger to contact each sheet fed into the accumulator by the roller, and to exert force to urge each sheet toward the lateral fence and the longitudinal fence of the accumulator. In an embodiment, the roller assembly includes a selectively rotating shaft. The cam is fixed with respect to the shaft, and the registration finger is mounted on the shaft. The registration finger can include a collar secured to the shaft, with a finger member adapted for contact with sheet material connected to the collar and a cam follower adapted for contact with the cam. The registration finger can be fabricated from a flexible plastic material, and the cam can be provided as a shaft bushing. A biasing mechanism can secured between the registration finger and the cam. The biasing mechanism can be provided as a compression spring biasing the registration finger into contact with the cam. A method of improving sheet registration in an imaging system including a roller assembly adapted to feed sheet material in the system into an accumulator is also provided.