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 $44.87   6.698%   $47.8754   $47.88   $47.90   $47.90  
  Purchase #2 $204.81   4.506%   $214.0387   $214.04   $214.05   $214.00  
  Purchase #3 $81.91   11.307%   $91.1716   $91.17   $91.15   $91.20  
  Purchase #4 $73.55   7.872%   $79.3399   $79.34   $79.35   $79.30  
  Purchase #5 $69.70   5.554%   $73.5711   $73.57   $73.55   $73.60  
  Purchase #6 $196.30   4.470%   $205.0746   $205.07   $205.05   $205.10  
  Purchase #7 $139.26   10.863%   $154.3878   $154.39   $154.40   $154.40  
  7 purchase totals = $810.40       $865.4591   $865.46   $865.45   $865.50