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 $239.75   10.823%   $265.6981   $265.70   $265.70   $265.70  
  Purchase #2 $24.79   5.689%   $26.2003   $26.20   $26.20   $26.20  
  Purchase #3 $40.60   6.159%   $43.1006   $43.10   $43.10   $43.10  
  Purchase #4 $146.77   13.617%   $166.7557   $166.76   $166.75   $166.80  
  Purchase #5 $159.72   11.627%   $178.2906   $178.29   $178.30   $178.30  
  Purchase #6 $70.45   12.116%   $78.9857   $78.99   $79.00   $79.00  
  Purchase #7 $42.99   6.448%   $45.762   $45.76   $45.75   $45.80  
  7 purchase totals = $725.07       $804.7930   $804.80   $804.80   $804.90