$tradedata = fread($file, 8192);
fclose($file);
$jsonTradedata = json_decode($tradedata, true);
mysql_query("UPDATE `websiteSettings` SET `tradeHillWorth` = '".$jsonTradedata['ticker']['last']."'");
echo $jsonTradedata['ticker']['last'];
This accessed a table in MySQL called websiteSettings in my main DB. You don't need a database, but it makes it easier to reduce load on your website because you can pool every N times, instead of every time the page loads.
Then you run this somewhere in your PHP code before you want to call the variable:
$tradeHillWorth = mysql_fetch_object($tradeHillQ);
Then you run this when you want to insert the price in the output of the HTML page:
The code above will round it to two decimal places. Again, this is very, very similar to how you would do it for any exchange. Just read their API documentation.