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 $14.86   9.821%   $16.3194   $16.32   $16.30   $16.30  
  Purchase #2 $46.73   8.597%   $50.7474   $50.75   $50.75   $50.70  
  Purchase #3 $34.41   5.602%   $36.3376   $36.34   $36.35   $36.30  
  Purchase #4 $192.48   4.501%   $201.1435   $201.14   $201.15   $201.10  
  Purchase #5 $181.27   9.616%   $198.7009   $198.70   $198.70   $198.70  
  Purchase #6 $60.63   9.855%   $66.6051   $66.61   $66.60   $66.60  
  Purchase #7 $25.60   3.868%   $26.5902   $26.59   $26.60   $26.60  
  7 purchase totals = $555.98       $596.4441   $596.45   $596.45   $596.30