Why doesn't my if-statements return the right numbers?

Question

First of all, this is my first week trying out C# or any other programming language for that matter, also my first post here on Stackoverflow!

Been working on this change calculator for a while now, trying to get it to round the result to either 0 if its <.25, 0.50 if it's between .25 and .75 and 1 if it's >.75. Seems like it's ignoring my if-statements, And on top of that the result I get isn't correct either. Some calculations ends up being negative, which I can't figure out why :/

        double summa0 = vara - kontant; //item - change
        var extrakt = (int)summa0; //removes decimals out of summa0 = 107
        var avrundsSumma = summa0 - extrakt; //<--- extracts the decimals out of summa0

        if (avrundsSumma < 0.25f)
        {
            avrundsSumma = Math.Floor(avrundsSumma);
        }
        else if (avrundsSumma > 0.75f)                          //Runs the decimals through if-statements
        {
            avrundsSumma = Math.Ceiling(avrundsSumma);
        }
        else
        {
            avrundsSumma = 0.5;
        }                                       // = in this case the result should be 1


        double summa = extrakt + avrundsSumma; // 107 + 1 = 108
        double attBetala = kontant - summa; // 500 - 108 = 392

Since I'm very new to this it's hard to know exactly which part of the code is causing the issue. When I run the code in CMD I get a negative result from "double summa = extrakt + avrundsSumma; // 107 + 1 = 108" So instead of 108 I get -108.

Not sure what you mean by "Hard code the values" either :o