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 $207.53   9.475%   $227.1935   $227.19   $227.20   $227.20  
  Purchase #2 $242.95   4.522%   $253.9362   $253.94   $253.95   $253.90  
  Purchase #3 $211.39   13.565%   $240.0651   $240.07   $240.05   $240.10  
  Purchase #4 $237.40   5.536%   $250.5425   $250.54   $250.55   $250.50  
  Purchase #5 $104.34   9.397%   $114.1448   $114.14   $114.15   $114.10  
  Purchase #6 $165.33   5.434%   $174.314   $174.31   $174.30   $174.30  
  Purchase #7 $15.91   10.401%   $17.5648   $17.56   $17.55   $17.60  
  7 purchase totals = $1,184.85       $1,277.7609   $1,277.75   $1,277.75   $1,277.70