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 $42.88   8.661%   $46.5938   $46.59   $46.60   $46.60  
  Purchase #2 $223.93   4.176%   $233.2813   $233.28   $233.30   $233.30  
  Purchase #3 $249.85   6.622%   $266.3951   $266.40   $266.40   $266.40  
  Purchase #4 $71.99   5.783%   $76.1532   $76.15   $76.15   $76.20  
  Purchase #5 $93.79   12.165%   $105.1996   $105.20   $105.20   $105.20  
  Purchase #6 $168.82   3.686%   $175.0427   $175.04   $175.05   $175.00  
  Purchase #7 $72.89   5.687%   $77.0353   $77.04   $77.05   $77.00  
  7 purchase totals = $924.15       $979.7010   $979.70   $979.75   $979.70