Payroll - Tax Withheld Differs to what was calculated a month ago

Hi, 

I am running the payroll for the last weeks of september and I noticed the payroll done for the previous weeks (from July to early September) shows a difference of $5 between the PAYG and the NET wage. 

The empoyee's wage is still the same for the whole period and no changes were done in the Employee details. 

See snapshots attached

TIA