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 $233.67   13.198%   $264.5098   $264.51   $264.50   $264.50  
  Purchase #2 $193.69   10.616%   $214.2521   $214.25   $214.25   $214.30  
  Purchase #3 $63.66   10.103%   $70.0916   $70.09   $70.10   $70.10  
  Purchase #4 $220.81   6.536%   $235.2421   $235.24   $235.25   $235.20  
  Purchase #5 $239.71   6.725%   $255.8305   $255.83   $255.85   $255.80  
  Purchase #6 $44.47   7.685%   $47.8875   $47.89   $47.90   $47.90  
  Purchase #7 $245.57   4.186%   $255.8496   $255.85   $255.85   $255.80  
  7 purchase totals = $1,241.58       $1,343.6632   $1,343.66   $1,343.70   $1,343.60