Point of order:
"I bribe the guards" is not a skill check. It is the route chosen when a) you failed an real skill check, like persuade or intimidate, or b) you are forgoing any attempts at a skill check because you either lack confidence in your abilities, just don't want to risk failing the attempt, or you just want to fast forward the plot. It has more to do with knowing the motives of the guards, unless you just want the dice to make that call for you. Which is also ok, I guess.
Case 1 (persuade check): "Hey, guards! I know you're loyal and honor bound by duty, and all that. But could I interest you in some gold to look away for a moment?" <roll whatever and explain to me how you are so persuasive that you can change someone's morals regardless of the amount offered>
Case 2 (intimidate check): "Hey, guards! Take this coin or I'll beat you with it!" <sounds like a no-brainer to me. If they were ever open to bribes in the first place, I think they'll just go with option a>
Case 3 (no checks): "Hey, guards! Have some money!" <toss them any amount. If they were corruptible to begin with, the only thing that matters is how much they can get>