This setup will show / hidden unit cost and edit / cannot edit unit cost when selling process.
1. Go to 'Configuration' from 'Setup' menu, and move into the 'POS' tab menu.
Setup Unit Cost
|Visible "YES"||Show your Unit Cost|
|Visible "NO"||Hidden your Unit Cost|
|Enabled "YES"||You can edit unit cost when selling process|
|Enabled "NO"||You cannot edit unit cost when selling process|
And you must untick role "Cost".
2. In the selling process