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 $24.41   9.537%   $26.738   $26.74   $26.75   $26.70  
  Purchase #2 $199.65   8.573%   $216.766   $216.77   $216.75   $216.80  
  Purchase #3 $203.36   8.508%   $220.6619   $220.66   $220.65   $220.70  
  Purchase #4 $176.26   3.349%   $182.1629   $182.16   $182.15   $182.20  
  Purchase #5 $30.28   13.845%   $34.4723   $34.47   $34.45   $34.50  
  Purchase #6 $187.34   11.693%   $209.2457   $209.25   $209.25   $209.20  
  Purchase #7 $32.46   6.387%   $34.5332   $34.53   $34.55   $34.50  
  7 purchase totals = $853.76       $924.5800   $924.58   $924.55   $924.60