Even in this condition a real coin minted under the rule of Emperor Nero isnt worthless. The coins from the juli-claudian dynasty are very wanted on the market. Iam no expert in prices but I think to have seen similiar conditioned coins sell on eBay for 15-25€.
Value left depends on it's denomination. Size and weight please, if it's around 30mm and over 20g it should be a sestertius, those are usually worth more than the smaller as and dupondius. As alfonz said it should be somewhere between 15 and 25e.
I collect and deal in ancient Roman coin. In case you're looking for affordable ancient coins or need any help with the coins you already have send me a message.
One of the keys to value is if the coin can be uniquely identified. Bust right on the obverse, and flying winged victory holding a shield between the letters S-C, appears on about a dozen coins. You might want to see if you can match any other features from your coin:
A quarter is I guess around 25mm which would make it too small to be a sestertii, my best guess is this is an As, something like RIC 312 on WildWinds. The same revers was commonly used for ases, dupondius and sestertii with the denomination being tied to it's size and weight not design.
Finding the exact RIC number would add the coin value but even without it it still has some value, I'd say around 10e being an As, if it was a sestertii it would be more. The emperor is clearly Nero, the reverse is Victory holding shield, it's a real ancient coin not a copy. Sure, the most hard core collectors wouldn't add it to their collection but a lot of collectors with a tight budget will find it desirable.
I collect and deal in ancient Roman coin. In case you're looking for affordable ancient coins or need any help with the coins you already have send me a message.