From my experience, SAL registered does not incur taxes (that or I've been hella lucky every time).
Shipping cost is WAY less than EMS BUT it does take significantly longer for the product to arrive. Where EMS will arrive within a week, SAL registered will take 3-4 times that at most. Also bare in mind SAL registered is only insured up to I think 8000 yen should the package get lost or damaged.
I have ordered anything from small figma figures to large AUTOart 1/18 cars from amiami and never had any problems being taxed or lost. However, both times I tried EMS, I got taxed.