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 $52.80   8.709%   $57.3984   $57.40   $57.40   $57.40  
  Purchase #2 $122.86   8.747%   $133.6066   $133.61   $133.60   $133.60  
  Purchase #3 $237.25   3.474%   $245.4921   $245.49   $245.50   $245.50  
  Purchase #4 $57.97   8.137%   $62.687   $62.69   $62.70   $62.70  
  Purchase #5 $172.99   7.444%   $185.8674   $185.87   $185.85   $185.90  
  Purchase #6 $71.89   8.285%   $77.8461   $77.85   $77.85   $77.80  
  Purchase #7 $78.59   3.303%   $81.1858   $81.19   $81.20   $81.20  
  7 purchase totals = $794.35       $844.0834   $844.10   $844.10   $844.10