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 $49.55   13.731%   $56.3537   $56.35   $56.35   $56.40  
  Purchase #2 $193.93   6.611%   $206.7507   $206.75   $206.75   $206.80  
  Purchase #3 $208.63   8.506%   $226.3761   $226.38   $226.40   $226.40  
  Purchase #4 $241.25   13.830%   $274.6149   $274.61   $274.60   $274.60  
  Purchase #5 $53.39   10.807%   $59.1599   $59.16   $59.15   $59.20  
  Purchase #6 $132.37   5.105%   $139.1275   $139.13   $139.15   $139.10  
  Purchase #7 $210.77   12.185%   $236.4523   $236.45   $236.45   $236.50  
  7 purchase totals = $1,089.89       $1,198.8351   $1,198.83   $1,198.85   $1,199.00