Revel Systems, the iPad Point of Sale (POS) platform that rivals Square, has raised roughly $100 million in Series C funding from New York City-based private equity firm Welsh, Carson, Anderson & Stowe and others. The round includes an initial $65 million investment from WCAS and an additional $25 million equity line available from WCAS. Sanjay Swani, a general partner at WCAS is joining Revel's board.