Yo, Zach -- Modern coins that you find in circulation are always worth face value. Your coin is worth 10 centavos, or one-tenth of a peso, in Mexico. Today, one Mexican peso is worth about 7 cents US, so one-tenth of a peso is worth about seven-tenths of a cent. This is true for circulated coins.
Enterprising coin dealers get uncirculated coins from banks and then sell them to collectors. These dealers know that collectors are willing to pay substantially more than face value to add nice looking coins to their collections. So, if a dealer can buy a coin for one cent and sell it for one dollar, and if the dealer can sell enough of them, then he or she has a viable business. The eBay web site has enabled lots of people to become coin dealers in this way. But don't be fooled. There is plenty of work involved in being a coin dealer.
Mexican 5, 10, 20, and 50 centavos coins all look about the same. The denomination is displayed as a large number on one side, and the Mexican eagle-snake-cactus design appears on the other side. The 5 and 10 centavos coins are made of stainless steel. The 20 and 50 centavos coins are made of aluminum bronze. All dates and all denominations have catalog values like this:
worn: less than $1 US dollar approximate catalog value
average circulated: less than $1
well preserved: less than $1
fully uncirculated: $1