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 $201.39   5.381%   $212.2268   $212.23   $212.25   $212.20  
  Purchase #2 $34.59   6.271%   $36.7591   $36.76   $36.75   $36.80  
  Purchase #3 $111.74   3.538%   $115.6934   $115.69   $115.70   $115.70  
  Purchase #4 $67.86   11.537%   $75.689   $75.69   $75.70   $75.70  
  Purchase #5 $248.44   5.369%   $261.7787   $261.78   $261.80   $261.80  
  Purchase #6 $236.83   5.324%   $249.4388   $249.44   $249.45   $249.40  
  Purchase #7 $221.31   8.259%   $239.588   $239.59   $239.60   $239.60  
  7 purchase totals = $1,122.16       $1,191.1738   $1,191.18   $1,191.25   $1,191.20