Do it the correct way and it should work in everything.
Code:
US Dollars<br/><span style="text-decoration:line-through;">$9.95</span>
You can also get fancy with css and make the strikethrough a different color.
Code:
US Dollars<br/><span style='color:red;text-decoration:line-through'><span style='color:black'>$9.95</span>
Even better than doing css inline is to put the style in a stylesheet and call it up with a class.