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 $61.90   10.111%   $68.1587   $68.16   $68.15   $68.20  
  Purchase #2 $127.57   6.855%   $136.3149   $136.31   $136.30   $136.30  
  Purchase #3 $181.70   3.736%   $188.4883   $188.49   $188.50   $188.50  
  Purchase #4 $124.38   9.339%   $135.9958   $136.00   $136.00   $136.00  
  Purchase #5 $107.86   5.779%   $114.0932   $114.09   $114.10   $114.10  
  Purchase #6 $85.45   9.189%   $93.302   $93.30   $93.30   $93.30  
  Purchase #7 $24.64   10.617%   $27.256   $27.26   $27.25   $27.30  
  7 purchase totals = $713.50       $763.6089   $763.61   $763.60   $763.70