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 $85.44   8.771%   $92.9339   $92.93   $92.95   $92.90  
  Purchase #2 $58.59   4.586%   $61.2769   $61.28   $61.30   $61.30  
  Purchase #3 $127.57   9.377%   $139.5322   $139.53   $139.55   $139.50  
  Purchase #4 $76.63   6.332%   $81.4822   $81.48   $81.50   $81.50  
  Purchase #5 $67.73   11.724%   $75.6707   $75.67   $75.65   $75.70  
  Purchase #6 $190.89   3.269%   $197.1302   $197.13   $197.15   $197.10  
  Purchase #7 $217.29   8.422%   $235.5902   $235.59   $235.60   $235.60  
  7 purchase totals = $824.14       $883.6163   $883.61   $883.70   $883.60