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 $207.46   4.449%   $216.6899   $216.69   $216.70   $216.70  
  Purchase #2 $250.95   4.633%   $262.5765   $262.58   $262.60   $262.60  
  Purchase #3 $53.55   11.320%   $59.6119   $59.61   $59.60   $59.60  
  Purchase #4 $41.70   7.784%   $44.9459   $44.95   $44.95   $44.90  
  Purchase #5 $109.97   9.340%   $120.2412   $120.24   $120.25   $120.20  
  Purchase #6 $146.69   11.744%   $163.9173   $163.92   $163.90   $163.90  
  Purchase #7 $68.54   12.106%   $76.8375   $76.84   $76.85   $76.80  
  7 purchase totals = $878.86       $944.8202   $944.83   $944.85   $944.70