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 $171.59   5.455%   $180.9502   $180.95   $180.95   $181.00  
  Purchase #2 $250.61   4.292%   $261.3662   $261.37   $261.35   $261.40  
  Purchase #3 $58.75   8.589%   $63.796   $63.80   $63.80   $63.80  
  Purchase #4 $185.55   6.321%   $197.2786   $197.28   $197.30   $197.30  
  Purchase #5 $78.73   3.796%   $81.7186   $81.72   $81.70   $81.70  
  Purchase #6 $122.85   7.289%   $131.8045   $131.80   $131.80   $131.80  
  Purchase #7 $56.99   6.483%   $60.6847   $60.68   $60.70   $60.70  
  7 purchase totals = $925.07       $977.5988   $977.60   $977.60   $977.70