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 $76.53   12.671%   $86.2271   $86.23   $86.25   $86.20  
  Purchase #2 $146.76   10.778%   $162.5778   $162.58   $162.60   $162.60  
  Purchase #3 $211.36   6.331%   $224.7412   $224.74   $224.75   $224.70  
  Purchase #4 $208.46   6.426%   $221.8556   $221.86   $221.85   $221.90  
  Purchase #5 $152.54   11.537%   $170.1385   $170.14   $170.15   $170.10  
  Purchase #6 $50.47   11.105%   $56.0747   $56.07   $56.05   $56.10  
  Purchase #7 $146.55   5.273%   $154.2776   $154.28   $154.30   $154.30  
  7 purchase totals = $992.67       $1,075.8925   $1,075.90   $1,075.95   $1,075.90