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 $234.84   9.522%   $257.2015   $257.20   $257.20   $257.20  
  Purchase #2 $49.91   11.730%   $55.7644   $55.76   $55.75   $55.80  
  Purchase #3 $46.40   9.326%   $50.7273   $50.73   $50.75   $50.70  
  Purchase #4 $76.84   6.256%   $81.6471   $81.65   $81.65   $81.60  
  Purchase #5 $56.41   4.797%   $59.116   $59.12   $59.10   $59.10  
  Purchase #6 $224.74   3.326%   $232.2149   $232.21   $232.20   $232.20  
  Purchase #7 $54.59   10.602%   $60.3776   $60.38   $60.40   $60.40  
  7 purchase totals = $743.73       $797.0488   $797.05   $797.05   $797.00