Your main problem here is going to be that D&D is designed under the assumption that every +1 is a 5% chunk. You'll run into some problems turning those into 10% chunks, as large differences in bonuses will rapidly lead to auto-successes and auto-failures.
I'll demonstrate with a low level example, a first level fighter in fullplate fighting his twin. Let's give him +1 BAB, +3 Str bonus, and weapon focus. That is a grand total of a +5 attack bonus.
Defensively let's give him fullplate (+8), a shield (+2), and dex (+1) for an AC of 16 (decreasing all ACs and target numbers by 5, as [MENTION=63245]Evenglare[/MENTION] suggested, since you are rolling d10's).
You'll notice that the fighter can't hit the opponent, unless a natural 10 is considered an auto-hit, and even then a 10% chance to hit someone of the same level is pretty sad.
Now we outfitted that fighter pretty well defensively, but giving him banded mail instead of fullplate still gives him an AC of 14 (5+6+1+2), which still only gets hit 20% of the time.
That same match-up using d20s, as it was designed, has 25% and 35% success rates, respectively. Substantially higher, though still something of a grind.
It only gets worse as levels increase and BAB and save bonuses diverge, unfortunately. If you thought you had it bad as a monk with only a +15 BAB at level 20 versus the fighter's +20, imagine how much worse that is now that it represents a 50% to-hit differential instead of 25%!