Versa Hatchback rims 15"x5.5" +40mm offset

[bboard]

Hi guys... looking for rims for winter tires on my parents car, but here's my dilemma. They already have 2 front winter tires on 15" OEM alloys and have been asking tire shop to mount/dismount every winter/spring.... now they are considering getting steel rims...

OEM alloy/steel is 15"x5.5" +40mm offset, now I know it's usually ok to run 0.5" wider (i.e. 15"x6" rims on same tires), but it is okay to have wider rims/tires on the front while the back remains the same?

15"x5.5" are so hard to find....

thanks!