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 $212.63   13.504%   $241.3436   $241.34   $241.35   $241.30  
  Purchase #2 $249.54   10.447%   $275.6094   $275.61   $275.60   $275.60  
  Purchase #3 $47.68   3.597%   $49.395   $49.40   $49.40   $49.40  
  Purchase #4 $153.55   7.271%   $164.7146   $164.71   $164.70   $164.70  
  Purchase #5 $13.77   3.598%   $14.2654   $14.27   $14.25   $14.30  
  Purchase #6 $206.81   7.583%   $222.4924   $222.49   $222.50   $222.50  
  Purchase #7 $7.52   8.855%   $8.1859   $8.19   $8.20   $8.20  
  7 purchase totals = $891.50       $976.0063   $976.01   $976.00   $976.00