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 $241.98   6.269%   $257.1497   $257.15   $257.15   $257.10  
  Purchase #2 $244.50   6.211%   $259.6859   $259.69   $259.70   $259.70  
  Purchase #3 $157.60   11.780%   $176.1653   $176.17   $176.15   $176.20  
  Purchase #4 $41.72   12.768%   $47.0468   $47.05   $47.05   $47.00  
  Purchase #5 $177.34   3.543%   $183.6232   $183.62   $183.60   $183.60  
  Purchase #6 $59.99   4.571%   $62.7321   $62.73   $62.75   $62.70  
  Purchase #7 $38.51   4.433%   $40.2171   $40.22   $40.20   $40.20  
  7 purchase totals = $961.64       $1,026.6201   $1,026.63   $1,026.60   $1,026.50