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 $239.95   13.861%   $273.2095   $273.21   $273.20   $273.20  
  Purchase #2 $66.48   4.456%   $69.4423   $69.44   $69.45   $69.40  
  Purchase #3 $56.96   4.142%   $59.3193   $59.32   $59.30   $59.30  
  Purchase #4 $10.43   11.632%   $11.6432   $11.64   $11.65   $11.60  
  Purchase #5 $41.63   8.832%   $45.3068   $45.31   $45.30   $45.30  
  Purchase #6 $242.44   9.563%   $265.6245   $265.62   $265.60   $265.60  
  Purchase #7 $198.53   5.122%   $208.6987   $208.70   $208.70   $208.70  
  7 purchase totals = $856.42       $933.2443   $933.24   $933.20   $933.10