Magento1.x only uses "round" for tax and decimal number method, but sometimes it causes wrong result.
Also some merchants use "floor" and "ceil" for discarding decimal numbers.
Is it possible to choose decimal discarding method via admin panel for M2?
If we do simply discard decimal numbers, converting currencies causes serious trouble.
For example, 99.99USD is 11,961.15JPY ( 1USD is 119.6235JPY ), but JPY does not use under decimal number. Then correct result is 11,961 JPY.
If "round" is used for discarding method, sometimes converting result is not correct.