The difference between "t" and "d" is one of voicing, not position of articulation; in English we emphasize the difference with aspiration of the unvoiced member of the pair. (What you're hearing as 'dime' could be 'time' with an unaspirated "t".) When people talk about tonguing differently using d and t it doesn't seem to make sense, since they're produced in the same location - any difference may have something to do with vocalic onset in the voiced d, a difference somewhere in the throat (preparing to activate the vocal cords). I'm trying out various tonguing positions with the trumpet, but my ear isn't good enough to really hear any difference in sound yet. Originally it wasn't good enough to hear the difference between the Russian dental t and the English palato-alveolar t, but my Russian teacher could hear it and would wince, so eventually I learned, in self-defense.