There are primary taps (assume off-load) that allow a voltage adjustment of plus or minus 5% from nominal (or from 95% to 105% of rated voltage), in 2.5% steps. So you will have the nominal center tap, then two taps above and two taps below the nominal voltage. So steps of 2.5%. This is totally standard. The best source of information is always the transformer nameplate. Maybe someone could take a picture for you. I wouldn't put too much faith in what is in this computer model, unless you are really sure of the source of the information.