Was there a 10 cent us currency in 1840?

Yes. The Coinage Act of 1792 put into production a "disme" which was one-tenth of a dollar and was 89.24% silver and 10.76% copper. However, the "dime" was not circulated until 1796. Since then, although the design has been changed several times, it has been minted almost every year. There has not been a year since then during which it was not in circulation, and it has always been worth either ten cents or 1/10th of a dollar.