Tariffs were collected where the imports entered the country. Since at least 90% of imports in 1860 entered through the North, it stands to reason that at least 90% of imports went to the North. Southern exports went out through southern ports, so imports to the South would have arrived at southern ports as well.
"Since at least 90% of imports in 1860 entered through the North, it stands to reason that at least 90% of imports went to the North."
What makes you think they stayed there?
Translation: "It is flatly untrue"