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 $113.34   10.566%   $125.3155   $125.32   $125.30   $125.30  
  Purchase #2 $205.91   12.338%   $231.3152   $231.32   $231.30   $231.30  
  Purchase #3 $152.99   7.726%   $164.81   $164.81   $164.80   $164.80  
  Purchase #4 $38.61   9.373%   $42.2289   $42.23   $42.25   $42.20  
  Purchase #5 $126.99   6.510%   $135.257   $135.26   $135.25   $135.30  
  Purchase #6 $240.70   8.489%   $261.133   $261.13   $261.15   $261.10  
  Purchase #7 $38.50   13.458%   $43.6813   $43.68   $43.70   $43.70  
  7 purchase totals = $917.04       $1,003.7409   $1,003.75   $1,003.75   $1,003.70