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 $60.57   8.418%   $65.6688   $65.67   $65.65   $65.70  
  Purchase #2 $72.58   5.583%   $76.6321   $76.63   $76.65   $76.60  
  Purchase #3 $240.49   7.574%   $258.7047   $258.70   $258.70   $258.70  
  Purchase #4 $71.54   13.433%   $81.15   $81.15   $81.15   $81.20  
  Purchase #5 $46.72   11.682%   $52.1778   $52.18   $52.20   $52.20  
  Purchase #6 $17.86   4.800%   $18.7173   $18.72   $18.70   $18.70  
  Purchase #7 $249.80   13.237%   $282.866   $282.87   $282.85   $282.90  
  7 purchase totals = $759.56       $835.9167   $835.92   $835.90   $836.00