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 $60.41   8.228%   $65.3805   $65.38   $65.40   $65.40  
  Purchase #2 $213.91   7.827%   $230.6527   $230.65   $230.65   $230.70  
  Purchase #3 $144.60   9.262%   $157.9929   $157.99   $158.00   $158.00  
  Purchase #4 $41.53   12.853%   $46.8679   $46.87   $46.85   $46.90  
  Purchase #5 $7.81   9.325%   $8.5383   $8.54   $8.55   $8.50  
  Purchase #6 $110.83   3.135%   $114.3045   $114.30   $114.30   $114.30  
  Purchase #7 $230.97   12.170%   $259.079   $259.08   $259.10   $259.10  
  7 purchase totals = $810.06       $882.8158   $882.81   $882.85   $882.90