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 $226.77   13.461%   $257.2955   $257.30   $257.30   $257.30  
  Purchase #2 $172.42   12.215%   $193.4811   $193.48   $193.50   $193.50  
  Purchase #3 $237.71   9.795%   $260.9937   $260.99   $261.00   $261.00  
  Purchase #4 $22.65   13.204%   $25.6407   $25.64   $25.65   $25.60  
  Purchase #5 $55.92   10.796%   $61.9571   $61.96   $61.95   $62.00  
  Purchase #6 $182.55   13.618%   $207.4097   $207.41   $207.40   $207.40  
  Purchase #7 $9.71   5.552%   $10.2491   $10.25   $10.25   $10.20  
  7 purchase totals = $907.73       $1,017.0269   $1,017.03   $1,017.05   $1,017.00