<?php

$data = array
(
    'USD',
    '10150.00',
    '9850.00',
    'SGD',
    '8015.40',
    '7915.40',
    'HKD',
    '1304.60',
    '1288.60',
);

$result = array();

while (is_null($value = array_shift($data)) !== true)
{
	if (preg_match('~^[A-Z]{3}$~', $value) > 0)
	{
		$result[$value] = array
		(
			'Buy' => array_shift($data),
			'Sell' => array_shift($data),
		);
	}
}

print_r($result); // transformed array