How do I get these columns to be equal size?

I have a site here http://174.132.164.189/~artofste/index.php?option=com_juliaportfolio&layout=detail&catid=1%3Apaintings&Itemid=54 that displays a series of paintings in columns.

I cannot get the columns to stay the same width. If you change the number of items displayed by changing the bottom dropdown to "10" and then jump to page 4 you can see it only has 3 paintings and they are bunched together.

Any help would be appreciated.

@CHARSET "UTF-8";
.portfolio
{
	margin: 0px 5px;
}
.portfolioitem
{
	margin-top: 0px;
	margin-bottom: 10px;
	text-align: center;
}
.itemimage
{
	background: #fff;
	padding: 7px;
	border: 1px solid #ccc;
	margin: 5px 10px;
}
.itemdescription
{
	text-align: center;
	color: #ccc;
	font-family: Arial, Helvetica, sans-serif;
	font-size: 13px;
	padding: 3px 5px;
}
.itemlink
{
}

.icon-48-portfolio
{
    background-image: url('../images/icon-48-portfolio.png');
}

div.portfolioitem {margin-left: auto; margin-right: auto;  width: 170px;}

.portfolioitem.col-1 {
  margin-right: 5px;

}

.colset-1 .col-1 {
  width: 19.3%;

}

.col-1,.col-2,.col-3,.col-4 ,.col-5 {
 float: left; 
  border: 1px solid white;
}

/**/
.colset-2 .col-1,.colset-2 .col-2 {
  width: 19.3%;
}

.colset-2 .col-2 {
  float: right;
}

/**/ /**/
.colset-3 .col-1,.colset-3 .col-2,.colset-3 .col-3 {
  width: 19.3%;
}

.colset-3 .col-3 {
  float: right;
}

/**/ /**/ /**/
.colset-4 .col-1,.colset-4 .col-2,.colset-4 .col-3, .colset-4 .col-4 {
  width: 19.3%;
}

.colset-4 .col-4 {
  float: right;
}

/**/ /**/ /**/  /**/
.colset-5 .col-1,.colset-5 .col-2,.colset-5 .col-3, .colset-5 .col-4, .colset-5 .col-5 {
  width: 19.3%;
}

.colset-5 .col-5 {
  float: right;
}

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