The Arduino documation for the Keyboard library lists 176 as mapping to `KEY_ENTER'.
The source code maps ASCII 10 to ENTER and does not map ASCII 13 to anything.
Internally both 176 and 10 map to the USB HID keyboard value 40 (decimal).
According to http://www.usb.org/developers/devclass_docs/Hut1_11.pdf 40 maps to "Keyboard Enter" (as opposed to "Keypad Enter")
So use either 176 or 10 they should do the same thing.