@calicojoy, from what I've read, some people report a change in taste while on prednisone. For some it can make food taste metallic. For sense of smell, an oral corticosteroid like prednisone can be used to stimulate the sense of smell for people who experience olfaction subtraction.
I suggest mentioning this side effect to your physician as prednisone may not be the cause. When did you start to notice the loss of smell and taste? Only when tapering down the dose of prednisone? What other changes were happening to your health at the time?