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 $112.73   11.394%   $125.5745   $125.57   $125.55   $125.60  
  Purchase #2 $59.57   8.346%   $64.5417   $64.54   $64.55   $64.50  
  Purchase #3 $40.26   3.641%   $41.7259   $41.73   $41.75   $41.70  
  Purchase #4 $60.90   9.702%   $66.8085   $66.81   $66.80   $66.80  
  Purchase #5 $71.46   4.771%   $74.8694   $74.87   $74.85   $74.90  
  Purchase #6 $171.91   8.175%   $185.9636   $185.96   $185.95   $186.00  
  Purchase #7 $115.93   5.699%   $122.5369   $122.54   $122.55   $122.50  
  7 purchase totals = $632.76       $682.0205   $682.02   $682.00   $682.00