SD, Great discussion.  I'll look-up the various state corporate tax rates to catch-up and get back to you.  I can only guess at national pricing strategy.  But I suspect it has a lot to do with standardization.  By that I mean, to give the customer the same "feeling" or should I say "experience" whether one is in Wyoming or Maine.  I would further guess it has to do with national advertising.  I also suspect they don't want someone from Oregon to be in Idaho and say, hey, we only pay $2.50 for that back home, lets go see what Wendy's has to offer next time and with that, brand loyalty becomes to crumble.  But notice that last sentence, price matters and if the competitor sees a way to safely undercut their competitor, everything begins to change.  Additionally, as business look more and more to increase sales and growth, they will look for all possible ways to lower costs and increase prices.  As a businessperson, I'm sure you know all of this.

See post below for state tax rates.