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 $135.93   11.458%   $151.5049   $151.50   $151.50   $151.50  
  Purchase #2 $208.68   13.109%   $236.0359   $236.04   $236.05   $236.00  
  Purchase #3 $18.63   5.278%   $19.6133   $19.61   $19.60   $19.60  
  Purchase #4 $108.37   10.337%   $119.5722   $119.57   $119.55   $119.60  
  Purchase #5 $184.57   13.586%   $209.6457   $209.65   $209.65   $209.60  
  Purchase #6 $42.53   3.864%   $44.1734   $44.17   $44.15   $44.20  
  Purchase #7 $199.81   6.847%   $213.491   $213.49   $213.50   $213.50  
  7 purchase totals = $898.52       $994.0364   $994.03   $994.00   $994.00