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 $180.89   8.771%   $196.7559   $196.76   $196.75   $196.80  
  Purchase #2 $245.73   11.211%   $273.2788   $273.28   $273.30   $273.30  
  Purchase #3 $188.81   5.519%   $199.2304   $199.23   $199.25   $199.20  
  Purchase #4 $84.94   8.493%   $92.154   $92.15   $92.15   $92.20  
  Purchase #5 $17.34   9.131%   $18.9233   $18.92   $18.90   $18.90  
  Purchase #6 $8.44   12.269%   $9.4755   $9.48   $9.50   $9.50  
  Purchase #7 $34.63   3.514%   $35.8469   $35.85   $35.85   $35.80  
  7 purchase totals = $760.78       $825.6648   $825.67   $825.70   $825.70