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 $109.95   8.689%   $119.5036   $119.50   $119.50   $119.50  
  Purchase #2 $62.48   10.302%   $68.9167   $68.92   $68.90   $68.90  
  Purchase #3 $215.71   6.126%   $228.9244   $228.92   $228.90   $228.90  
  Purchase #4 $31.30   10.741%   $34.6619   $34.66   $34.65   $34.70  
  Purchase #5 $106.61   7.565%   $114.675   $114.68   $114.70   $114.70  
  Purchase #6 $23.65   6.554%   $25.2   $25.20   $25.20   $25.20  
  Purchase #7 $129.99   3.409%   $134.4214   $134.42   $134.40   $134.40  
  7 purchase totals = $679.69       $726.3030   $726.30   $726.25   $726.30