Tipping is a discretionary and optional gift; however, it is certainly welcomed at resort-style hotels in Mexico. Most guests will tip 10-15% of their final bill, and/or 50-100 pesos for a la carte services like room service delivery (around $2-5 USD).
If the hotel leaves an envelope for you at the end of your stay, this is a subtle gesture to incentivize a tip if you are satisfied. But! Keep in mind that some all-inclusive hotels will automatically add gratuity. Always confirm the distribution of your original payment at the time of booking to ensure you are not tipping twice!