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 $196.99   13.786%   $224.147   $224.15   $224.15   $224.10  
  Purchase #2 $90.66   5.302%   $95.4668   $95.47   $95.45   $95.50  
  Purchase #3 $8.40   13.555%   $9.5386   $9.54   $9.55   $9.50  
  Purchase #4 $163.88   10.258%   $180.6908   $180.69   $180.70   $180.70  
  Purchase #5 $105.34   11.686%   $117.65   $117.65   $117.65   $117.70  
  Purchase #6 $152.89   13.730%   $173.8818   $173.88   $173.90   $173.90  
  Purchase #7 $151.95   6.386%   $161.6535   $161.65   $161.65   $161.70  
  7 purchase totals = $870.11       $963.0285   $963.03   $963.05   $963.10