By John Dickey/The Union Bed tax revenue figures suggest that tourism in Nevada County may have suffered from the same post-Sept. 11 slowdown that hit major California tourist destinations such as San Francisco. Both Grass Valley and Nevada City reported lower bed tax figures during the fourth quarter of 2001, as compared with 2000. The 10 percent tax on lodging - called the transient occupancy tax - is levied on rooms rented by hotels, motels and bed-and-breakfast inns. It provides a rough gauge of visits from people who live more than a day trip from the area. Annual figures for …