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 $56.86   7.572%   $61.1654   $61.17   $61.15   $61.20  
  Purchase #2 $101.74   3.645%   $105.4484   $105.45   $105.45   $105.40  
  Purchase #3 $69.38   10.373%   $76.5768   $76.58   $76.60   $76.60  
  Purchase #4 $47.81   4.298%   $49.8649   $49.86   $49.85   $49.90  
  Purchase #5 $164.48   8.457%   $178.3901   $178.39   $178.40   $178.40  
  Purchase #6 $235.28   11.675%   $262.7489   $262.75   $262.75   $262.70  
  Purchase #7 $184.75   9.629%   $202.5396   $202.54   $202.55   $202.50  
  7 purchase totals = $860.30       $936.7341   $936.74   $936.75   $936.70