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 $221.89   4.827%   $232.6006   $232.60   $232.60   $232.60  
  Purchase #2 $46.75   8.269%   $50.6158   $50.62   $50.60   $50.60  
  Purchase #3 $183.67   8.331%   $198.9715   $198.97   $198.95   $199.00  
  Purchase #4 $92.54   12.377%   $103.9937   $103.99   $104.00   $104.00  
  Purchase #5 $238.99   4.786%   $250.4281   $250.43   $250.45   $250.40  
  Purchase #6 $124.26   12.428%   $139.703   $139.70   $139.70   $139.70  
  Purchase #7 $26.83   4.130%   $27.9381   $27.94   $27.95   $27.90  
  7 purchase totals = $934.93       $1,004.2508   $1,004.25   $1,004.25   $1,004.20