If you paused the moment you conquered the last country, its still showing pre-conquest figures. All data is at least for the previous day, and some of it takes longer to be recalculated. The trade page is quite capable of getting stuck in normal play and might be stuck permanently when there is no trade or you might be able to get it to update by jumping around different pages. A couple of days played at world domination should see tariffs disappear from the budget page, until then its still using the last days trading with the last remaining nation(s) in its predicction of the current day's trading.