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 $34.57   11.200%   $38.4418   $38.44   $38.45   $38.40  
  Purchase #2 $221.76   7.135%   $237.5826   $237.58   $237.60   $237.60  
  Purchase #3 $180.77   8.721%   $196.535   $196.54   $196.55   $196.50  
  Purchase #4 $249.93   7.580%   $268.8747   $268.87   $268.85   $268.90  
  Purchase #5 $72.78   4.731%   $76.2232   $76.22   $76.20   $76.20  
  Purchase #6 $174.42   10.680%   $193.0481   $193.05   $193.05   $193.00  
  Purchase #7 $242.53   12.337%   $272.4509   $272.45   $272.45   $272.50  
  7 purchase totals = $1,176.76       $1,283.1563   $1,283.15   $1,283.15   $1,283.10