I'm assuming you're referring to regular price (selling price), not sale price. Sale price would be regular price crossed out and a discounted (sale) price shown next to it.
NOTE: this will update your regular price, it has nothing to do with sale prices.
The following SQL query ran from admin->Tools->Install SQL Patches should do the trick (please make sure you backup your database BEFORE running any SQL queries in case something goes wrong):
Code:
UPDATE products set products_price = products_price * 1.05 WHERE manufacturers_id = '123';
You will, of course, need to change the text in red to match your manufacturers ID