This question is essentially impossible to answer. Apart from “Ancient Rome” being ill-defined (that's at least a 1000-year time span...): the value of goods changed a lot since then (and the answer would depend on whether you choose “as much gold as $10 can buy today” or “as much wheat as $10 can buy today” or “as many kittens as $10 can buy today”...). Actually, the most meaningful way to define an equivalent of today's $10 would be “whichever amount gets you as far as $10 gets you today”, which would immediately answer your question (but quite unsatisfactorily).