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 $232.67   12.257%   $261.1884   $261.19   $261.20   $261.20  
  Purchase #2 $190.73   9.323%   $208.5118   $208.51   $208.50   $208.50  
  Purchase #3 $67.73   9.427%   $74.1149   $74.11   $74.10   $74.10  
  Purchase #4 $242.67   7.603%   $261.1202   $261.12   $261.10   $261.10  
  Purchase #5 $186.70   10.823%   $206.9065   $206.91   $206.90   $206.90  
  Purchase #6 $230.93   3.749%   $239.5876   $239.59   $239.60   $239.60  
  Purchase #7 $149.58   3.655%   $155.0471   $155.05   $155.05   $155.00  
  7 purchase totals = $1,301.01       $1,406.4765   $1,406.48   $1,406.45   $1,406.40