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 $22.48   9.122%   $24.5306   $24.53   $24.55   $24.50  
  Purchase #2 $121.83   8.114%   $131.7153   $131.72   $131.70   $131.70  
  Purchase #3 $130.50   12.339%   $146.6024   $146.60   $146.60   $146.60  
  Purchase #4 $249.40   3.665%   $258.5405   $258.54   $258.55   $258.50  
  Purchase #5 $45.69   8.415%   $49.5348   $49.53   $49.55   $49.50  
  Purchase #6 $206.26   12.791%   $232.6427   $232.64   $232.65   $232.60  
  Purchase #7 $144.36   5.732%   $152.6347   $152.63   $152.65   $152.60  
  7 purchase totals = $920.52       $996.2010   $996.19   $996.25   $996.00