Thanks to all for the replies. I will bring USD from home and use them for the tips. No charge ATM's allow me to get cash for no fee, unlike the ATM'S in Europe which charge for the privilege.
So far the TD (while American) have resided in the country of the tour and the same for the drivers. It seems to me only appropriate to tip in the currency of the tour. Otherwise they are being penalized when they convert the currency. Unless, of course, you are being extra generous and taking this into account.