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 $136.72   12.367%   $153.6282   $153.63   $153.65   $153.60  
  Purchase #2 $92.61   9.738%   $101.6284   $101.63   $101.65   $101.60  
  Purchase #3 $220.93   5.373%   $232.8006   $232.80   $232.80   $232.80  
  Purchase #4 $67.53   13.822%   $76.864   $76.86   $76.85   $76.90  
  Purchase #5 $184.54   9.767%   $202.564   $202.56   $202.55   $202.60  
  Purchase #6 $69.97   4.704%   $73.2614   $73.26   $73.25   $73.30  
  Purchase #7 $76.85   9.204%   $83.9233   $83.92   $83.90   $83.90  
  7 purchase totals = $849.15       $924.6699   $924.66   $924.65   $924.70