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 $250.49   4.513%   $261.7946   $261.79   $261.80   $261.80  
  Purchase #2 $169.31   3.712%   $175.5948   $175.59   $175.60   $175.60  
  Purchase #3 $125.85   8.540%   $136.5976   $136.60   $136.60   $136.60  
  Purchase #4 $111.80   6.583%   $119.1598   $119.16   $119.15   $119.20  
  Purchase #5 $108.69   6.234%   $115.4657   $115.47   $115.45   $115.50  
  Purchase #6 $72.64   5.383%   $76.5502   $76.55   $76.55   $76.60  
  Purchase #7 $108.37   6.291%   $115.1876   $115.19   $115.20   $115.20  
  7 purchase totals = $947.15       $1,000.3503   $1,000.35   $1,000.35   $1,000.50