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 $23.94   8.403%   $25.9517   $25.95   $25.95   $26.00  
  Purchase #2 $87.99   6.383%   $93.6064   $93.61   $93.60   $93.60  
  Purchase #3 $239.43   9.277%   $261.6419   $261.64   $261.65   $261.60  
  Purchase #4 $127.26   8.214%   $137.7131   $137.71   $137.70   $137.70  
  Purchase #5 $86.61   13.752%   $98.5206   $98.52   $98.50   $98.50  
  Purchase #6 $48.89   9.724%   $53.6441   $53.64   $53.65   $53.60  
  Purchase #7 $138.81   12.854%   $156.6526   $156.65   $156.65   $156.70  
  7 purchase totals = $752.93       $827.7304   $827.72   $827.70   $827.70