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 $75.95   8.285%   $82.2425   $82.24   $82.25   $82.20  
  Purchase #2 $140.27   10.111%   $154.4527   $154.45   $154.45   $154.50  
  Purchase #3 $26.85   12.624%   $30.2395   $30.24   $30.25   $30.20  
  Purchase #4 $18.86   8.503%   $20.4637   $20.46   $20.45   $20.50  
  Purchase #5 $84.58   13.134%   $95.6887   $95.69   $95.70   $95.70  
  Purchase #6 $108.25   10.120%   $119.2049   $119.20   $119.20   $119.20  
  Purchase #7 $244.76   8.801%   $266.3013   $266.30   $266.30   $266.30  
  7 purchase totals = $699.52       $768.5933   $768.58   $768.60   $768.60