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 $208.56   6.648%   $222.4251   $222.43   $222.45   $222.40  
  Purchase #2 $6.73   8.172%   $7.28   $7.28   $7.30   $7.30  
  Purchase #3 $11.33   11.874%   $12.6753   $12.68   $12.70   $12.70  
  Purchase #4 $149.98   3.194%   $154.7704   $154.77   $154.75   $154.80  
  Purchase #5 $195.78   12.181%   $219.628   $219.63   $219.65   $219.60  
  Purchase #6 $217.90   4.597%   $227.9169   $227.92   $227.90   $227.90  
  Purchase #7 $163.37   12.624%   $183.9938   $183.99   $184.00   $184.00  
  7 purchase totals = $953.65       $1,028.6895   $1,028.70   $1,028.75   $1,028.70