1. Navigate to Setup > Users/Roles > Manage Roles.
2. Edit the Custom Role.
3. Navigate to Permissions tab > Reports subtab and add the following:
Sales Order Transaction Report
Sales Order Reports Report
Sales Order Fulfillment Reports
4. Set the Level of Permission to View.
5. Hit Save.
For complete list of Permission please topic "Permissions Documentation " (SuiteAnswer ID 9911)