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 $249.49   7.268%   $267.6229   $267.62   $267.60   $267.60  
  Purchase #2 $53.77   13.554%   $61.058   $61.06   $61.05   $61.10  
  Purchase #3 $56.79   7.118%   $60.8323   $60.83   $60.85   $60.80  
  Purchase #4 $247.53   4.714%   $259.1986   $259.20   $259.20   $259.20  
  Purchase #5 $125.76   11.807%   $140.6085   $140.61   $140.60   $140.60  
  Purchase #6 $136.58   12.328%   $153.4176   $153.42   $153.40   $153.40  
  Purchase #7 $49.98   12.594%   $56.2745   $56.27   $56.25   $56.30  
  7 purchase totals = $919.90       $999.0124   $999.01   $998.95   $999.00