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 $227.74   5.826%   $241.0081   $241.01   $241.00   $241.00  
  Purchase #2 $143.57   6.865%   $153.4261   $153.43   $153.45   $153.40  
  Purchase #3 $187.72   5.838%   $198.6791   $198.68   $198.70   $198.70  
  Purchase #4 $5.99   4.577%   $6.2642   $6.26   $6.25   $6.30  
  Purchase #5 $87.77   11.719%   $98.0558   $98.06   $98.05   $98.10  
  Purchase #6 $78.49   4.258%   $81.8321   $81.83   $81.85   $81.80  
  Purchase #7 $169.28   10.383%   $186.8563   $186.86   $186.85   $186.90  
  7 purchase totals = $900.56       $966.1217   $966.13   $966.15   $966.20