Two problems: Problem one:

value += 0.1f;

is sometimes adding 0.10000001. Problem two:

    if (value <= 0.1f)
        render.material = tenC;
    else if (value > 0.1f && value < 0.5f)
        render.material = twentyC;
    else if (value > 0.4f && value < 1f)
        render.material = fiftyC;
    else if(value > 0.9f)
        render.material = oneDollar;

When value goes back down to 0.1, it doesn't set the material to tenC.