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 $164.41   6.534%   $175.1525   $175.15   $175.15   $175.20  
  Purchase #2 $63.50   8.763%   $69.0645   $69.06   $69.05   $69.10  
  Purchase #3 $181.46   5.582%   $191.5891   $191.59   $191.60   $191.60  
  Purchase #4 $120.70   13.847%   $137.4133   $137.41   $137.40   $137.40  
  Purchase #5 $250.37   6.130%   $265.7177   $265.72   $265.70   $265.70  
  Purchase #6 $30.56   12.608%   $34.413   $34.41   $34.40   $34.40  
  Purchase #7 $8.68   6.537%   $9.2474   $9.25   $9.25   $9.20  
  7 purchase totals = $819.68       $882.5975   $882.59   $882.55   $882.60