5% space is reserved for root, you also have to account for the size of the journal. As for the display of 60GB used... you sure you're not getting confused between GB and GiB?
1GiB=1,073,741,824 bytes (=1024x1024x1024 bytes).
The difference is that GB is straight metric base 10 and GiB "gibibyte" is an approximation of metric in base 2. When you have a hard disk that is labeled as 1TB, thats 1,000,000,000,000 bytes. When you look at the capacity using df or gparted, the size you see will be somewhat smaller because of this conversion. And to get really confusing, sometimes (most of the time), software will display units in GiB, but label them as GB. The reason for this is that GB (and other associated binary prefixes) were used to state values in base 2. The prefix GiB, MiB, KiB, etc., were only introduced in 1999 and to this date have not entirely caught on.