<button onclick="degistir('x', 0.05)">X Arttır</button>
<button onclick="degistir('x', -0.05)">X Azalt</button>
<button onclick="degistir('y', 0.05)">Y Arttır</button>
<button onclick="degistir('y', -0.05)">Y Azalt</button>

var var1 = 0.95;
var var2 = 0.85;
function degistir(yer, miktar) {
       var1 = yer == "x" ? var1+miktar : var1;
       var2 = yer == "y" ? var2+miktar : var2;
      document.getElementById("divID").style.transform = "scale("+var1+", "+var2+")";
}