Domestic manufactures raise, or keep prices up to the tariff level, so they are not voluntary as there is no way to avoid them.
Buy the import, pay the tariff. Buy the domestic, pay the price very very close to the tariff.
An increase in prices would depend on the number of domestic companies and business engaged in producing the same product, Markets are not suspended because there are no competing imports, far from it, a business concern in WA can still easily out compete a business in say NY simply because of the differences in State and Local taxes and regulatory burdens and mandates.
The real difference would come in the “who” was making the profits, small businesses or global corporations.
It's should be surprising that the argument that tariffs are "free" often comes coupled with the argument that tariffs "protect high-paying jobs." Think about that for a minute. If either, or both, arguments are true, we should raise tariffs 1000% across the board.