JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://thepantrybromley.com/home/css/responsive-grid/responsivegridsystem.css">
<link rel="stylesheet" href="http://thepantrybromley.com/home/css/pantry-custom.css">
<hr />
<div>
    <span>&pound;</span><span id='number'>0.00</span>
</div>
<hr />
<div class="section group">
	<div class="col span_1_of_5">
		<div class='button_epos_e button_epos_e-border dn'>
			<div class='button_epos_e_content'>
				Button
			</div>
		</div>
	</div>
	
	<div class="col span_1_of_5">
		<div id='pay_7' class='button_epos_e button_epos_e-border'>
			<div class='button_epos_e_content'>
				7
			</div>
		</div>
	</div>
	
	<div class="col span_1_of_5">
		<div id='pay_8' class='button_epos_e button_epos_e-border'>
			<div class='button_epos_e_content'>
				8
			</div>
		</div>
	</div>
	
	<div class="col span_1_of_5">
		<div id='pay_9' class='button_epos_e button_epos_e-border'>
			<div class='button_epos_e_content'>
				9
			</div>
		</div>
	</div>
	
	<div class="col span_1_of_5">
		<div class='button_epos_e button_epos_e-border dn'>
			<div class='button_epos_e_content'>
				Button
			</div>
		</div>
	</div>
</div>

<div style='clear: both;'></div>

<div class="section group">
	<div class="col span_1_of_5">
		<div class='button_epos_e button_epos_e-border dn'>
			<div class='button_epos_e_content'>
				Button
			</div>
		</div>
	</div>
	
	<div class="col span_1_of_5">
		<div id='pay_4' class='button_epos_e button_epos_e-border'>
			<div class='button_epos_e_content'>
				4
			</div>
		</div>
	</div>
	
	<div class="col span_1_of_5">
		<div id='pay_5' class='button_epos_e button_epos_e-border'>
			<div class='button_epos_e_content'>
				5
			</div>
		</div>
	</div>
	
	<div class="col span_1_of_5">
		<div id='pay_6' class='button_epos_e button_epos_e-border'>
			<div class='button_epos_e_content'>
				6
			</div>
		</div>
	</div>
	
	<div class="col span_1_of_5">
		<div class='button_epos_e button_epos_e-border dn'>
			<div...

CSS

.dn {
    display: none;
}
/*  GRID OF FIVE   ============================================================================= */

	
.span_5_of_5 {
	width: 100%;
}

.span_4_of_5 {
  	width: 79.68%; 
}

.span_3_of_5 {
  	width: 59.36%; 
}

.span_2_of_5 {
  	width: 39.04%;
}

.span_1_of_5 {
  	width: 18.72%;
}


/*  GO FULL WIDTH AT LESS THAN 480 PIXELS */

@media only screen and (max-width: 480px) {
	.span_5_of_5 {
		width: 100%; 
	}
	.span_4_of_5 {
		width: 100%; 
	}
	.span_3_of_5 {
		width: 100%; 
	}
	.span_2_of_5 {
		width: 100%; 
	}
	.span_1_of_5 {
		width: 100%; 
	}
}
/*  SECTIONS  */
.section {
	clear: both;
	padding: 0px;
	margin: 0px;
}

/*  COLUMN SETUP  */
.col {
	display: block;
	float:left;
	margin: 1% 0 1% 1.6%;
}
.col:first-child { margin-left: 0; }


/*  GROUPING  */
.group:before,
.group:after {
	content:"";
	display:table;
}
.group:after {
	clear:both;
}
.group {
    zoom:1; /* For IE 6/7 */
}

JavaScript

$(".button_epos_e").click( function() {
   
    btn_id = $(this).attr("id");                          
    btn_num = btn_id.replace("pay_", "");
     alert(btn_num);
    
    decimal = $("#number").text();
    // alert(decimal);
    var truenumber = decimal.replace(".", "");
    // alert(truenumber);
    
    truenumber += btn_num;
     //alert(truenumber);
   
    postDecimal = truenumber.slice(-2);
    // alert(postDecimal);
    preDecimal = truenumber.replace(postDecimal, "");
    preDecInt = parseInt(preDecimal);
    // alert(preDecimal);
    newDecimal = preDecimal+"."+postDecimal;
    
    $("#number").html(newDecimal);  
    
    
});