I frequently buy domain names from GoDaddy and I always use this set of codes depending on which will save me the most money:

• OYH1 - 10% off whatever
• OYH2 - $5 off a $30 purchase
• OYH3 - $3 off / $6.95 any .COM (renewals too… just used it)

Most likely OYH3 will be your best bet, as it always give you 6.95 domains. Have fun!