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 $236.67   5.443%   $249.5519   $249.55   $249.55   $249.60  
  Purchase #2 $57.73   4.629%   $60.4023   $60.40   $60.40   $60.40  
  Purchase #3 $113.31   8.490%   $122.93   $122.93   $122.95   $122.90  
  Purchase #4 $72.36   6.434%   $77.0156   $77.02   $77.00   $77.00  
  Purchase #5 $156.66   7.709%   $168.7369   $168.74   $168.75   $168.70  
  Purchase #6 $40.88   11.297%   $45.4982   $45.50   $45.50   $45.50  
  Purchase #7 $246.45   6.497%   $262.4619   $262.46   $262.45   $262.50  
  7 purchase totals = $924.06       $986.5968   $986.60   $986.60   $986.60