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 $247.70   8.661%   $269.1533   $269.15   $269.15   $269.20  
  Purchase #2 $55.80   5.724%   $58.994   $58.99   $59.00   $59.00  
  Purchase #3 $223.26   6.406%   $237.562   $237.56   $237.55   $237.60  
  Purchase #4 $87.95   5.136%   $92.4671   $92.47   $92.45   $92.50  
  Purchase #5 $28.44   8.751%   $30.9288   $30.93   $30.95   $30.90  
  Purchase #6 $131.77   7.357%   $141.4643   $141.46   $141.45   $141.50  
  Purchase #7 $163.30   9.758%   $179.2348   $179.23   $179.25   $179.20  
  7 purchase totals = $938.22       $1,009.8043   $1,009.79   $1,009.80   $1,009.90