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 $14.93   3.318%   $15.4254   $15.43   $15.45   $15.40  
  Purchase #2 $130.77   7.161%   $140.1344   $140.13   $140.15   $140.10  
  Purchase #3 $61.28   11.852%   $68.5429   $68.54   $68.55   $68.50  
  Purchase #4 $201.57   3.311%   $208.244   $208.24   $208.25   $208.20  
  Purchase #5 $248.93   5.462%   $262.5266   $262.53   $262.55   $262.50  
  Purchase #6 $249.26   7.399%   $267.7027   $267.70   $267.70   $267.70  
  Purchase #7 $216.40   9.737%   $237.4709   $237.47   $237.45   $237.50  
  7 purchase totals = $1,123.14       $1,200.0469   $1,200.04   $1,200.10   $1,199.90