Using five identical tyres is a good and very sound practice. It is especially important for all-terrain vehicles.

When five identical tyres are being used, they need to be periodically rotated in a "five tyre rotation scheme", which is even clearly explained in Jimny's owner's manuals.

Using five tyres instead of four is actually cheaper in the long term!

Read the wiki page "Tyre selection and usage - best practices" for the hands-on practical guide.