Since my previous cute, easy number puzzle turned out to be a duplicate, I felt I needed to redeem myself.
$2+9 = 6$
$7+8 = 8$
$9+6 = 5$
$0+9 = 6$
$1+4 = 6$
$9+9 = 3$
$2+6 = 6$
$6+4 = 7$
$1+5 = 6$
@TroyAndAbed:
$12+27 = 8$
What does:
$5+5 = ?$
Why?
Hopefully isn't too hard, please ask if you need any test cases.
HINT 1
Use the title of the question