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 $84.58   13.498%   $95.9966   $96.00   $96.00   $96.00  
  Purchase #2 $124.39   9.677%   $136.4272   $136.43   $136.45   $136.40  
  Purchase #3 $185.37   12.616%   $208.7563   $208.76   $208.75   $208.80  
  Purchase #4 $105.87   13.713%   $120.388   $120.39   $120.40   $120.40  
  Purchase #5 $87.74   3.292%   $90.6284   $90.63   $90.65   $90.60  
  Purchase #6 $40.32   6.320%   $42.8682   $42.87   $42.85   $42.90  
  Purchase #7 $76.64   3.841%   $79.5837   $79.58   $79.60   $79.60  
  7 purchase totals = $704.91       $774.6484   $774.66   $774.70   $774.70