Hi Tanya,
SAP generally follows the lifecycle extended support dates published by Microsoft, though of course there are restrictions within given NetWeaver releases. The published lifecycle dates for SQL Server 2005 are at http://support2.microsoft.com/lifecycle/?p1=2855. From this you can see that Extended Support for SQL 2005 ends 4/12/2016.
Naturally, you must also check the PAM for your particular NetWeaver release. I don't think SQL 2014 is generally released for SAP products yet, except by special agreement. I've been migrating my SQL 2005 systems to SQL 2012 over the past few and upcoming months with good success.
Regards,
Matt