IMTU, the basis of the taxes for Imperial citizens is a transactional tax. You use the Imperial Credit - for anything - you pay for the privilege. In peacetime, it's a 1% transactional tax; in wartime it is 1.5% and has gone as high as 2% when the Imperium has gotten desperate.
1% tax, you ask!?!? That's
NOTHING, you say??!?
It would be if it was a sales tax, but it's a
transactional tax. Here's how it works for the purchase of a Cr 1 pencil in a spaceport's gift shop:
You buy the pencil, using a Credit, which costs you Cr 0.01 in tax. The shopkeeper also pays Cr 0.01 in tax for getting the money.
When the shopkeeper bought the pencil (which only cost him 1/2 a Cr), he paid another 0.005 in tax on it, and so did the warehouse he bought it from.
The warehouse, which bought it
en masse from the wholesaler, paid only 0.1 Cr per pencil, which was another 2 x 0.001 Cr for tax.
The factory paid its workers their salaries, etc., to produce the pencil, and each of those transactions was taxed, but the part that applies to the cost of the pencil was another 0.05 Cr for the actual cost of making the pencil, which is another 2 x 0.0005 Cr for tax.
0.0005 x 2 + 0.001 x 2 + 0.005 x 2 + 0.01 x 2
is 0.033 Cr in tax on a 1 Cr pencil, all told. And this isn't a very "deep" example, where you'd have to look at the cost of food for the lumberjack, salaries, etc., all of which are taxed that little bit for the privilege of using the Credit.
Sure, the vendors all pass on the cost of the tax to the next guy, and it's included in that Cr 1 cost for convenience's sake.
Bottom line - I charge straight prices for things, and assume the tax is included. Now, if the players want to barter and avoid using the Credit, they can do so, but even specie will fill up a ship's cargo hold pretty darned fast. The only way to deal with HUGE amounts of money is electronically.
My Cr 0.02 for the day