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 $243.58   8.789%   $264.9882   $264.99   $265.00   $265.00  
  Purchase #2 $87.27   4.137%   $90.8804   $90.88   $90.90   $90.90  
  Purchase #3 $32.77   8.353%   $35.5073   $35.51   $35.50   $35.50  
  Purchase #4 $182.29   6.395%   $193.9474   $193.95   $193.95   $193.90  
  Purchase #5 $29.66   5.304%   $31.2332   $31.23   $31.25   $31.20  
  Purchase #6 $73.88   3.838%   $76.7155   $76.72   $76.70   $76.70  
  Purchase #7 $92.58   12.285%   $103.9535   $103.95   $103.95   $104.00  
  7 purchase totals = $742.03       $797.2255   $797.23   $797.25   $797.20