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 $23.91   11.637%   $26.6924   $26.69   $26.70   $26.70  
  Purchase #2 $201.67   6.809%   $215.4017   $215.40   $215.40   $215.40  
  Purchase #3 $98.56   3.193%   $101.707   $101.71   $101.70   $101.70  
  Purchase #4 $62.82   6.169%   $66.6954   $66.70   $66.70   $66.70  
  Purchase #5 $228.29   4.470%   $238.4946   $238.49   $238.50   $238.50  
  Purchase #6 $232.80   3.873%   $241.8163   $241.82   $241.80   $241.80  
  Purchase #7 $59.38   10.757%   $65.7675   $65.77   $65.75   $65.80  
  7 purchase totals = $907.43       $956.5749   $956.58   $956.55   $956.60