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 $226.89   9.614%   $248.7032   $248.70   $248.70   $248.70  
  Purchase #2 $9.44   8.165%   $10.2108   $10.21   $10.20   $10.20  
  Purchase #3 $107.43   11.579%   $119.8693   $119.87   $119.85   $119.90  
  Purchase #4 $121.65   11.603%   $135.765   $135.77   $135.75   $135.80  
  Purchase #5 $81.49   5.771%   $86.1928   $86.19   $86.20   $86.20  
  Purchase #6 $213.38   10.429%   $235.6334   $235.63   $235.65   $235.60  
  Purchase #7 $104.65   8.724%   $113.7797   $113.78   $113.80   $113.80  
  7 purchase totals = $864.93       $950.1542   $950.15   $950.15   $950.20