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 $204.98   7.457%   $220.2654   $220.27   $220.25   $220.30  
  Purchase #2 $107.39   5.726%   $113.5392   $113.54   $113.55   $113.50  
  Purchase #3 $71.41   6.439%   $76.0081   $76.01   $76.00   $76.00  
  Purchase #4 $42.94   6.373%   $45.6766   $45.68   $45.70   $45.70  
  Purchase #5 $105.55   8.373%   $114.3877   $114.39   $114.40   $114.40  
  Purchase #6 $9.72   7.721%   $10.4705   $10.47   $10.45   $10.50  
  Purchase #7 $226.63   8.858%   $246.7049   $246.70   $246.70   $246.70  
  7 purchase totals = $768.62       $827.0524   $827.06   $827.05   $827.10