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 $56.42   11.577%   $62.9517   $62.95   $62.95   $63.00  
  Purchase #2 $240.87   8.739%   $261.9196   $261.92   $261.90   $261.90  
  Purchase #3 $221.35   8.866%   $240.9749   $240.97   $240.95   $241.00  
  Purchase #4 $236.41   6.224%   $251.1242   $251.12   $251.10   $251.10  
  Purchase #5 $216.33   4.393%   $225.8334   $225.83   $225.85   $225.80  
  Purchase #6 $115.80   7.296%   $124.2488   $124.25   $124.25   $124.20  
  Purchase #7 $214.27   8.681%   $232.8708   $232.87   $232.85   $232.90  
  7 purchase totals = $1,301.45       $1,399.9234   $1,399.91   $1,399.85   $1,399.90