Modern maybe, but before OT existed ties weren't rare. Out of curiosity I looked it up: In 1973, the last year before OT was implemented, three teams had two ties. Since 74, only one season had two games end in a tie, 1986 (different teams). The Packers lead the NFL in ties since '74, with five. The record for most ties in a season, the 1932 Bears, with six.