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 $60.31   13.309%   $68.3367   $68.34   $68.35   $68.30  
  Purchase #2 $22.99   7.599%   $24.737   $24.74   $24.75   $24.70  
  Purchase #3 $103.76   9.422%   $113.5363   $113.54   $113.55   $113.50  
  Purchase #4 $107.38   11.389%   $119.6095   $119.61   $119.60   $119.60  
  Purchase #5 $104.45   7.779%   $112.5752   $112.58   $112.60   $112.60  
  Purchase #6 $210.39   12.748%   $237.2105   $237.21   $237.20   $237.20  
  Purchase #7 $63.42   6.571%   $67.5873   $67.59   $67.60   $67.60  
  7 purchase totals = $672.70       $743.5925   $743.61   $743.65   $743.50