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 $32.70   4.752%   $34.2539   $34.25   $34.25   $34.30  
  Purchase #2 $224.85   5.362%   $236.9065   $236.91   $236.90   $236.90  
  Purchase #3 $133.30   4.763%   $139.6491   $139.65   $139.65   $139.60  
  Purchase #4 $171.92   8.538%   $186.5985   $186.60   $186.60   $186.60  
  Purchase #5 $50.69   5.421%   $53.4379   $53.44   $53.45   $53.40  
  Purchase #6 $180.50   12.543%   $203.1401   $203.14   $203.15   $203.10  
  Purchase #7 $10.49   9.531%   $11.4898   $11.49   $11.50   $11.50  
  7 purchase totals = $804.45       $865.4758   $865.48   $865.50   $865.40