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 $248.85   8.258%   $269.4   $269.40   $269.40   $269.40  
  Purchase #2 $24.57   6.739%   $26.2258   $26.23   $26.25   $26.20  
  Purchase #3 $107.26   7.737%   $115.5587   $115.56   $115.55   $115.60  
  Purchase #4 $154.45   4.808%   $161.876   $161.88   $161.90   $161.90  
  Purchase #5 $121.57   11.619%   $135.6952   $135.70   $135.70   $135.70  
  Purchase #6 $169.44   11.200%   $188.4173   $188.42   $188.40   $188.40  
  Purchase #7 $43.58   6.181%   $46.2737   $46.27   $46.25   $46.30  
  7 purchase totals = $869.72       $943.4467   $943.46   $943.45   $943.50