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 $93.70   4.266%   $97.6972   $97.70   $97.70   $97.70  
  Purchase #2 $173.30   13.477%   $196.6556   $196.66   $196.65   $196.70  
  Purchase #3 $122.41   3.681%   $126.9159   $126.92   $126.90   $126.90  
  Purchase #4 $222.89   11.706%   $248.9815   $248.98   $249.00   $249.00  
  Purchase #5 $54.29   8.556%   $58.9351   $58.94   $58.95   $58.90  
  Purchase #6 $183.56   6.407%   $195.3207   $195.32   $195.30   $195.30  
  Purchase #7 $38.86   4.713%   $40.6915   $40.69   $40.70   $40.70  
  7 purchase totals = $889.01       $965.1975   $965.21   $965.20   $965.20