It's pretty much certain that you won't have $10,000 in the face value of the coins due to their weight ($10,000 in dimes weighs 225kg/500 lbs, more for other coins or mixes).
If you aren't sure you can just declare them at customs and give them a general description ('about 5 lbs of old coins' or '10 mint sets and a bag of other old ones') and then they can decide if it's worth looking at more or not. If you declare them, even if they end up being incredibly valuable, you won't get in trouble even if you guessed wrong as to what they are or their value.
Last edited by bpe; Jun 18, 2019 at 8:12 pm