When Romney is asked did he pay any taxes for 10 years, and he answers, "I paid taxes I was required to pay", it wouldn't be a lie. Because he could simply say I meant 2010 to 2011. Ask him did he pay taxes from 1999 to 2009, and any years in between. Then notice his response.
All he has to say, if challenged as it stand now, I was asked did I pay any taxes at all in 10 years. He could get away with the answer he gives now. If he respond to the question as it pertain to years 1999 to 2009, and he says, i paid the required taxes, he would be lying if he didn't pay. Ask the right questions, because liars think in manipulative ways.