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 $58.95   3.383%   $60.9443   $60.94   $60.95   $60.90  
  Purchase #2 $245.67   6.246%   $261.0145   $261.01   $261.00   $261.00  
  Purchase #3 $40.44   12.676%   $45.5662   $45.57   $45.55   $45.60  
  Purchase #4 $202.78   9.546%   $222.1374   $222.14   $222.15   $222.10  
  Purchase #5 $193.32   8.859%   $210.4462   $210.45   $210.45   $210.40  
  Purchase #6 $60.34   8.872%   $65.6934   $65.69   $65.70   $65.70  
  Purchase #7 $123.81   4.674%   $129.5969   $129.60   $129.60   $129.60  
  7 purchase totals = $925.31       $995.3989   $995.40   $995.40   $995.30