Owlbear Rodeo supports a physically simulated 3D dice tray and dice. To access these features click the Show Dice Tray icon in the top left of the map view.
A running total of how many dice you have added will show up above each dice icon.
Once your dice have been rolled a calculated total of the dice can be seen on the bottom of the dice tray.
To reroll all your dice you can click the Reroll Dice icon in the bottom right of the dice tray if you wish to reroll a single die you can simply grab the dice and throw it in the dice tray.