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 $249.25   10.208%   $274.6934   $274.69   $274.70   $274.70  
  Purchase #2 $176.95   10.786%   $196.0358   $196.04   $196.05   $196.00  
  Purchase #3 $170.34   12.225%   $191.1641   $191.16   $191.15   $191.20  
  Purchase #4 $182.95   5.831%   $193.6178   $193.62   $193.60   $193.60  
  Purchase #5 $5.64   8.446%   $6.1164   $6.12   $6.10   $6.10  
  Purchase #6 $84.58   13.739%   $96.2004   $96.20   $96.20   $96.20  
  Purchase #7 $78.37   9.577%   $85.8755   $85.88   $85.90   $85.90  
  7 purchase totals = $948.08       $1,043.7034   $1,043.71   $1,043.70   $1,043.70