When doing a transaction, the system will store the tax of every item in that transaction up to 2 rounding decimals. The calculation of total tax for a day would be summing up all the tax that the system stored on each item. So the sum up amount will be a little bit different than the amount that you divided by 1.06 because it only store up to 2 rounding decimals.
Example of a Daily Sales Report:
Here the 1038.50 is the total sales included tax, if you calculate the 6% tax from 1038.50 it will be 58.78(1038.5-1038.5/1.06).