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 $23.48   3.733%   $24.3565   $24.36   $24.35   $24.40  
  Purchase #2 $182.28   4.766%   $190.9675   $190.97   $190.95   $191.00  
  Purchase #3 $206.60   4.396%   $215.6821   $215.68   $215.70   $215.70  
  Purchase #4 $164.63   6.551%   $175.4149   $175.41   $175.40   $175.40  
  Purchase #5 $242.75   12.727%   $273.6448   $273.64   $273.65   $273.60  
  Purchase #6 $146.32   4.799%   $153.3419   $153.34   $153.35   $153.30  
  Purchase #7 $248.66   5.293%   $261.8216   $261.82   $261.80   $261.80  
  7 purchase totals = $1,214.72       $1,295.2293   $1,295.22   $1,295.20   $1,295.20