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 $90.44   6.462%   $96.2842   $96.28   $96.30   $96.30  
  Purchase #2 $190.70   4.447%   $199.1804   $199.18   $199.20   $199.20  
  Purchase #3 $40.98   11.541%   $45.7095   $45.71   $45.70   $45.70  
  Purchase #4 $105.64   9.835%   $116.0297   $116.03   $116.05   $116.00  
  Purchase #5 $171.41   12.606%   $193.0179   $193.02   $193.00   $193.00  
  Purchase #6 $196.83   5.125%   $206.9175   $206.92   $206.90   $206.90  
  Purchase #7 $42.99   11.445%   $47.9102   $47.91   $47.90   $47.90  
  7 purchase totals = $838.99       $905.0494   $905.05   $905.05   $905.00