I recommend not connecting NC pins at all.
Using NC pins in your layout may prove fatal later if you need to replace the original chip for whatever reason by a compatible chip. A compatible chip (new revision by same manufacturer or model by another manufacturer) may make use of that NC pin(s). This use of the former NC pin is likely not compatible with your layout.
If this is a one off project then these considerations are moot, of course.
Why would a compatible chip use a pin that is NC one the original model? One reason my be, just for example, that another manufacturer uses the original NC pin to trim the circuit on the chip to improve performance over the original chip. Or to add functionality, e.g.monitoring an internal circuit point etc. etc.