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 $240.96   3.623%   $249.69   $249.69   $249.70   $249.70  
  Purchase #2 $112.27   6.525%   $119.5956   $119.60   $119.60   $119.60  
  Purchase #3 $70.42   3.706%   $73.0298   $73.03   $73.05   $73.00  
  Purchase #4 $208.64   3.474%   $215.8882   $215.89   $215.90   $215.90  
  Purchase #5 $101.38   10.540%   $112.0655   $112.07   $112.05   $112.10  
  Purchase #6 $179.71   7.550%   $193.2781   $193.28   $193.30   $193.30  
  Purchase #7 $131.30   6.392%   $139.6927   $139.69   $139.70   $139.70  
  7 purchase totals = $1,044.68       $1,103.2399   $1,103.25   $1,103.30   $1,103.30