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 $126.46   10.866%   $140.2011   $140.20   $140.20   $140.20  
  Purchase #2 $70.91   8.230%   $76.7459   $76.75   $76.75   $76.70  
  Purchase #3 $55.34   7.620%   $59.5569   $59.56   $59.55   $59.60  
  Purchase #4 $208.27   6.426%   $221.6534   $221.65   $221.65   $221.70  
  Purchase #5 $143.49   4.266%   $149.6113   $149.61   $149.60   $149.60  
  Purchase #6 $123.43   10.527%   $136.4235   $136.42   $136.40   $136.40  
  Purchase #7 $121.54   13.317%   $137.7255   $137.73   $137.75   $137.70  
  7 purchase totals = $849.44       $921.9176   $921.92   $921.90   $921.90