We would advise giving your accountant access to the reports and accounting menus only. That should be sufficient to prepare your tax returns. 

To do this, please login and visit Admin >>  Manage Staff >> Staff Roles and Permissions. There create a new role called Accountant. Click Set Permissions button next to Accountant role and then check the relevant options. 

Then go to Admin >> Manage Staff >> Staff and click Add Staff button. There in Staff Role field, select Accountant.