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 $130.35   9.188%   $142.3266   $142.33   $142.35   $142.30  
  Purchase #2 $113.32   8.239%   $122.6564   $122.66   $122.65   $122.70  
  Purchase #3 $68.37   6.246%   $72.6404   $72.64   $72.65   $72.60  
  Purchase #4 $236.32   12.475%   $265.8009   $265.80   $265.80   $265.80  
  Purchase #5 $109.64   11.616%   $122.3758   $122.38   $122.40   $122.40  
  Purchase #6 $130.26   9.455%   $142.5761   $142.58   $142.60   $142.60  
  Purchase #7 $67.66   10.564%   $74.8076   $74.81   $74.80   $74.80  
  7 purchase totals = $855.92       $943.1838   $943.20   $943.25   $943.20