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 $87.77   8.151%   $94.9241   $94.92   $94.90   $94.90  
  Purchase #2 $69.78   6.501%   $74.3164   $74.32   $74.30   $74.30  
  Purchase #3 $15.96   5.614%   $16.856   $16.86   $16.85   $16.90  
  Purchase #4 $43.76   12.873%   $49.3932   $49.39   $49.40   $49.40  
  Purchase #5 $28.92   6.819%   $30.8921   $30.89   $30.90   $30.90  
  Purchase #6 $248.32   5.405%   $261.7417   $261.74   $261.75   $261.70  
  Purchase #7 $125.77   4.853%   $131.8736   $131.87   $131.85   $131.90  
  7 purchase totals = $620.28       $659.9971   $659.99   $659.95   $660.00