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 $64.44   4.358%   $67.2483   $67.25   $67.25   $67.20  
  Purchase #2 $138.66   10.611%   $153.3732   $153.37   $153.35   $153.40  
  Purchase #3 $147.88   4.283%   $154.2137   $154.21   $154.20   $154.20  
  Purchase #4 $34.70   3.546%   $35.9305   $35.93   $35.95   $35.90  
  Purchase #5 $248.39   4.549%   $259.6893   $259.69   $259.70   $259.70  
  Purchase #6 $206.99   12.614%   $233.0997   $233.10   $233.10   $233.10  
  Purchase #7 $7.38   3.664%   $7.6504   $7.65   $7.65   $7.70  
  7 purchase totals = $848.44       $911.2051   $911.20   $911.20   $911.20