[Dilettante_Pro]

Вот такой кривой костыль.

<style>
div {display:inline-block;
height:100px;
width:100px;
border:1px solid grey;
transition-property: border-radius;
transition-duration: 2s;
}
.mover {
   border:2px solid red;
   border-radius:30px;
}
</style>
<div></div>
<div></div>
<div></div>
<div></div>
<div></div>
<script>
var elems = document.querySelectorAll('div');
[].forEach.call(elems, function(it) {
   it.onmouseover = function() {
      for(var i = 0;i < elems.length; i++) {
         elems[i].classList.add('mover');
         if(elems[i] == it) break;
       }
   }
   it.onmouseleave = function() {
      for(var i = 0;i < elems.length; i++) {
           elems[i].classList.remove('mover');
      }
   }
});
</script>