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 $57.30   13.747%   $65.177   $65.18   $65.20   $65.20  
  Purchase #2 $240.85   8.664%   $261.7172   $261.72   $261.70   $261.70  
  Purchase #3 $125.85   9.291%   $137.5427   $137.54   $137.55   $137.50  
  Purchase #4 $170.80   8.528%   $185.3658   $185.37   $185.35   $185.40  
  Purchase #5 $14.66   9.202%   $16.009   $16.01   $16.00   $16.00  
  Purchase #6 $79.38   8.565%   $86.1789   $86.18   $86.20   $86.20  
  Purchase #7 $174.35   12.234%   $195.68   $195.68   $195.70   $195.70  
  7 purchase totals = $863.19       $947.6706   $947.68   $947.70   $947.70