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 $233.31   11.855%   $260.9689   $260.97   $260.95   $261.00  
  Purchase #2 $232.77   11.686%   $259.9715   $259.97   $259.95   $260.00  
  Purchase #3 $63.93   9.710%   $70.1376   $70.14   $70.15   $70.10  
  Purchase #4 $236.90   10.712%   $262.2767   $262.28   $262.30   $262.30  
  Purchase #5 $176.66   4.378%   $184.3942   $184.39   $184.40   $184.40  
  Purchase #6 $70.64   4.353%   $73.715   $73.72   $73.70   $73.70  
  Purchase #7 $114.48   3.839%   $118.8749   $118.87   $118.85   $118.90  
  7 purchase totals = $1,128.69       $1,230.3388   $1,230.34   $1,230.30   $1,230.40