It's recommended that you buy pesos before you land in Mexico, just in case you need the cash. According to this USA Today article, the most economical way to do this is to buy pesos from your bank in the U.S. Most banks will do this for free, especially if you're not withdrawing a significant amount of money.
Use the Local Currency
The local currency in Tulum is Mexican pesos. Tourists often use US dollars to avoid the hassle of currency exchange and calculations
In most tourist areas in Mexico, it is acceptable to tip in either pesos or dollars, though pesos are more practical for the person being tipped. If you do tip in dollars, be sure to only tip using notes and not coins as coins cannot be exchanged.
The best way to acquire pesos in Mexico for your trip is to utilize your debit card at an ATM. We recommend exchanging enough pesos from your home country before your trip to cover your initial expenses. Afterward, simply withdraw cash from a local ATM to obtain the most favorable exchange rate. It's advisable to withdraw cash early in the morning or during cooler hours, such as around 6 or 7 PM, to avoid the harsh sun and potential long lines, especially during high season.
It's just safer not to carry large amounts of cash on you in Mexico. Also, any cash you take out in your home country will have to be converted to pesos, and that conversion will cost you money