Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $55.57   10.427%   $61.3643   $61.36   $61.35   $61.40  
  Purchase #2 $116.96   12.713%   $131.8291   $131.83   $131.85   $131.80  
  Purchase #3 $150.91   12.436%   $169.6772   $169.68   $169.70   $169.70  
  Purchase #4 $67.99   10.631%   $75.218   $75.22   $75.20   $75.20  
  Purchase #5 $109.78   11.477%   $122.3795   $122.38   $122.40   $122.40  
  Purchase #6 $219.98   6.544%   $234.3755   $234.38   $234.40   $234.40  
  Purchase #7 $24.62   13.677%   $27.9873   $27.99   $28.00   $28.00  
  7 purchase totals = $745.81       $822.8309   $822.84   $822.90   $822.90