They are good for the whole meal with tax and tip as far as I know. You just hand them your vouchers to pay.
The vouchers on LastMinuteTravel for the non-premium is $30.66 and $15.82 with Getawaytoday at $31 and $16. These do include tax and tip, too. The premium price is $37.58 and $19.78 - I am not clear which are regular and premium, but dinner would be a premium versus Breakfast etc.