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 $23.57   10.517%   $26.0489   $26.05   $26.05   $26.00  
  Purchase #2 $232.93   12.396%   $261.804   $261.80   $261.80   $261.80  
  Purchase #3 $177.83   12.673%   $200.3664   $200.37   $200.35   $200.40  
  Purchase #4 $115.35   3.190%   $119.0297   $119.03   $119.05   $119.00  
  Purchase #5 $20.91   13.609%   $23.7556   $23.76   $23.75   $23.80  
  Purchase #6 $117.37   12.226%   $131.7197   $131.72   $131.70   $131.70  
  Purchase #7 $220.66   9.691%   $242.0442   $242.04   $242.05   $242.00  
  7 purchase totals = $908.62       $1,004.7685   $1,004.77   $1,004.75   $1,004.70