Actually you may have to 'waste' a roll of film because the only way to know if the 90mm center filter is appropriate for the 105mm lens is by testing it... In practice, it's not waste. It's testing, something that's inevitable with photography. Film is simply the cost of testing film cameras.
Center filters compensate for light fall off on wide angle lenses. The 90 is optimized for the 90mm lens. However, it may very well work for the 105 just as well. In fact, I don't know if there is a 105mm center filter. There may, there may not. I had the 90mm lens, and the center filter is indispensable with it. I did not have the 105mm lens so I can't comment on that.
Center filters are quite expensive. New, the Fuji ones were around $300. So if the 90 works on the 105, you'll save some money.
