Centering content of div in a container

In my website, i have a series of divs like this:

.box{
   float:left;
   width:143px;
   height:183px;
   overflow:hidden;
}

These divs are inside a simple container like this:

.container{
   margin:70px 190px 0 190px;
   overflow:hidden;
}

I would realize a responsive layout but the divs are not horizontal centered in the container. I tried to add "margin-left:auto;" and "margin-right:auto" but nothing. I have a layout as this:

Instead, i would a layout as this:

Can someone help me?