From my point of view, SJIS is correct.
Here is an example of SJIS locale usage written by [Red Hat](https://access.redhat.com/solutions/727043) and [HP-UX](https://web.archive.org/web/20061206132454/http://docs.hp.com/en/UXL10N-9030...) (see Appendix A).
Historically, until around 2000, the Japanese UNIX environment mainly used an encoding different from Shift-JIS, called EUC-JP (Extended Unix Code for Japanese). Therefore, with the exception of HP-UX, SJIS has rarely been used in locale settings.