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 $88.63   9.278%   $96.8531   $96.85   $96.85   $96.90  
  Purchase #2 $234.30   10.536%   $258.9858   $258.99   $259.00   $259.00  
  Purchase #3 $38.32   9.583%   $41.9922   $41.99   $42.00   $42.00  
  Purchase #4 $235.35   5.593%   $248.5131   $248.51   $248.50   $248.50  
  Purchase #5 $41.84   11.699%   $46.7349   $46.73   $46.75   $46.70  
  Purchase #6 $61.82   3.376%   $63.907   $63.91   $63.90   $63.90  
  Purchase #7 $123.97   12.807%   $139.8468   $139.85   $139.85   $139.80  
  7 purchase totals = $824.23       $896.8329   $896.83   $896.85   $896.80