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 $241.87   8.281%   $261.8993   $261.90   $261.90   $261.90  
  Purchase #2 $47.97   4.132%   $49.9521   $49.95   $49.95   $50.00  
  Purchase #3 $192.55   3.458%   $199.2084   $199.21   $199.20   $199.20  
  Purchase #4 $214.79   6.336%   $228.3991   $228.40   $228.40   $228.40  
  Purchase #5 $225.95   7.307%   $242.4602   $242.46   $242.45   $242.50  
  Purchase #6 $125.40   6.806%   $133.9347   $133.93   $133.95   $133.90  
  Purchase #7 $83.95   10.332%   $92.6237   $92.62   $92.60   $92.60  
  7 purchase totals = $1,132.48       $1,208.4775   $1,208.47   $1,208.45   $1,208.50