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 $241.30   10.216%   $265.9512   $265.95   $265.95   $266.00  
  Purchase #2 $69.27   10.284%   $76.3937   $76.39   $76.40   $76.40  
  Purchase #3 $148.90   9.727%   $163.3835   $163.38   $163.40   $163.40  
  Purchase #4 $75.46   13.400%   $85.5716   $85.57   $85.55   $85.60  
  Purchase #5 $86.65   8.656%   $94.1504   $94.15   $94.15   $94.20  
  Purchase #6 $247.72   5.858%   $262.2314   $262.23   $262.25   $262.20  
  Purchase #7 $90.93   8.653%   $98.7982   $98.80   $98.80   $98.80  
  7 purchase totals = $960.23       $1,046.4800   $1,046.47   $1,046.50   $1,046.60