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 $242.39   9.308%   $264.9517   $264.95   $264.95   $265.00  
  Purchase #2 $175.54   8.677%   $190.7716   $190.77   $190.75   $190.80  
  Purchase #3 $193.56   12.710%   $218.1615   $218.16   $218.15   $218.20  
  Purchase #4 $195.92   4.421%   $204.5816   $204.58   $204.60   $204.60  
  Purchase #5 $61.59   12.612%   $69.3577   $69.36   $69.35   $69.40  
  Purchase #6 $232.93   12.313%   $261.6107   $261.61   $261.60   $261.60  
  Purchase #7 $16.87   7.661%   $18.1624   $18.16   $18.15   $18.20  
  7 purchase totals = $1,118.80       $1,227.5972   $1,227.59   $1,227.55   $1,227.80