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 $211.63   7.552%   $227.6123   $227.61   $227.60   $227.60  
  Purchase #2 $123.97   11.806%   $138.6059   $138.61   $138.60   $138.60  
  Purchase #3 $43.70   6.775%   $46.6607   $46.66   $46.65   $46.70  
  Purchase #4 $19.46   11.419%   $21.6821   $21.68   $21.70   $21.70  
  Purchase #5 $45.33   7.115%   $48.5552   $48.56   $48.55   $48.60  
  Purchase #6 $91.75   12.545%   $103.26   $103.26   $103.25   $103.30  
  Purchase #7 $190.60   8.649%   $207.085   $207.09   $207.10   $207.10  
  7 purchase totals = $726.44       $793.4612   $793.47   $793.45   $793.60