Is the ignition switch ever been replace on the car, or is it the SAME ignition switch that came with the car when you bought it...that is did the locks work previously?? If it's the same key for the doors & the ignition switch, then it's possible that the tumblers in the door locks are dirty/frozen in place. Try hosing them down with some silicone spray, placing the key in them & see if the key will turn the cylinder lock. If not you might have to take the cylinder lock apart & see if there is any gunk/debris lodged in there. It's been a while since I've done that but that usually fixs the problems when I have key issues with my buddies cars. A REAL locksmith knows this & shouldn't have any problems fixing/rekeying locks on a car. Worst case scenario...buy a whole new lockset from Courtesy Nissan Parts ....
Nissan Parts, NISMO and Nissan Accessories - Courtesyparts.com.
Hope this helps....
ID