Some reports are configured to report totals at an item level that include tax, in these instances users may see a variance from the transaction level totals due to rounding.
At the PLU movement level tax is calculated at the individual PLU level and so there is sometimes a rounding variance, as in actuality tax is applied at a transaction level.
For example, consider the case of the following three items, where the the tax rate is is 8.875%:
Item 1 12.82
Item 2 13.25
Item 3 17.35
At a transaction level you have a total of 43.42 and tax of 3.85, however if you calculate the tax at a PLU level for report purposes; then you get a total of 3.86 after rounding calculated tax at each PLU level.
Again this happens because tax is calculated and rounded at a transaction level.