How do I use Highcharts to display candlestick with small values?

Question

You should use parseFloat() to change string into number for Ask / High values.

data.push([
         parseInt(jsonData[i].InserTime.substr(6)),
         parseFloat(jsonData[i].Ask),
         parseFloat(jsonData[i].High),
         parseFloat(jsonData[i].Low),
         parseFloat(jsonData[i].Bid)]);

Here's a full example:

HTML:

<div class="graphs">
    <div id="chartEURUSDContainer" style="height: 331px; min-width: 611px"></div>
</div>
<script src="http://ajax.aspnetcdn.com/ajax/jquery/jquery-1.9.0.min.js"
type="text/javascript"></script>
<script src="http://code.highcharts.com/stock/highstock.js"></script>
<script src="http://code.highcharts.com/stock/modules/exporting.js"></script>

Javascript:

 $(function () {

     var jsonData = [{
         "LastModification": "04:18:45",
         "Symbol": "EURUSD",
         "Bid": "1.33132",
         "Ask": "1.33157",
         "High": "1.33336",
         "Low": "1.33007",
         "Direction": "0",
         "InserTime": "\/Date(1358760060933)\/"
     }, {
         "LastModification": "04:20:05",
         "Symbol": "EURUSD",
         "Bid": "1.33151",
         "Ask": "1.33174",
         "High": "1.33336",
         "Low": "1.33007",
         "Direction": "0",
         "InserTime": "\/Date(1358760140625)\/"
     }, {
         "LastModification": "04:21:25",
         "Symbol": "EURUSD",
         "Bid": "1.3312",
         "Ask": "1.33144",
         "High": "1.33336",
         "Low": "1.33007",
         "Direction": "1",
         "InserTime": "\/Date(1358760220731)\/"
     }, {
         "LastModification": "04:22:48",
         "Symbol": "EURUSD",
         "Bid": "1.33115",
         "Ask": "1.33141",
         "High": "1.33336",
         "Low": "1.33007",
         "Direction": "-1",
         "InserTime": "\/Date(1358760300387)\/"
     }, {
         "LastModification": "04:23:48",
         "Symbol": "EURUSD",
         "Bid": "1.33107",
         "Ask": "1.33132",
         "High": "1.33336",
         "Low": "1.33007",
         "Direction": "-1",
         "InserTime": "\/Date(1358760361033)\/"
     }, {
         "LastModification": "04:25:08",
         "Symbol": "EURUSD",
         "Bid": "1.33139",
         "Ask": "1.33164",
         "High": "1.33336",
         "Low": "1.33007",
         "Direction": "0",
         "InserTime": "\/Date(1358760440193)\/"
     }, {
         "LastModification": "04:26:28",
         "Symbol": "EURUSD",
         "Bid": "1.33202",
         "Ask": "1.33222",
         "High": "1.33336",
         "Low": "1.33007",
         "Direction": "1",
         "InserTime": "\/Date(1358760520037)\/"
     }, {
         "LastModification": "04:27:48",
         "Symbol": "EURUSD",
         "Bid": "1.33212",
         "Ask": "1.33238",
         "High": "1.33336",
         "Low": "1.33007",
         "Direction": "-1",
         "InserTime": "\/Date(1358760600163)\/"
     }]

     var data = [];

     fillData();

     function fillData() {
         for (i = 0; i < jsonData.length; i++) {
             data.push([
             parseInt(jsonData[i].InserTime.substr(6)),
             parseFloat(jsonData[i].Ask),
             parseFloat(jsonData[i].High),
             parseFloat(jsonData[i].Low),
             parseFloat(jsonData[i].Bid)]);
 }
 CreateChart();
 }

 function CreateChart() {
     // create the chart
     chart = new Highcharts.StockChart({
         chart: {
             renderTo: 'chartEURUSDContainer',
             type: 'candlestick',
             marginRight: 10,
         },
         rangeSelector: {
             enabled: false
         },
         scrollbar: {
             enabled: false
         },
         navigator: {
             enabled: false
         },
         series: [{
             type: 'candlestick',
             color: '#00FF00',
             name: 'Currency Rates',
             data: data,

         }]
     });
 }
 });

Demo on JS Fiddle.