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 $103.76   10.577%   $114.7347   $114.73   $114.75   $114.70  
  Purchase #2 $185.47   8.144%   $200.5747   $200.57   $200.55   $200.60  
  Purchase #3 $11.68   3.323%   $12.0681   $12.07   $12.05   $12.10  
  Purchase #4 $70.31   7.538%   $75.61   $75.61   $75.60   $75.60  
  Purchase #5 $117.79   8.194%   $127.4417   $127.44   $127.45   $127.40  
  Purchase #6 $177.47   11.852%   $198.5037   $198.50   $198.50   $198.50  
  Purchase #7 $241.53   8.326%   $261.6398   $261.64   $261.65   $261.60  
  7 purchase totals = $908.01       $990.5727   $990.56   $990.55   $990.50