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 $24.47   9.396%   $26.7692   $26.77   $26.75   $26.80  
  Purchase #2 $236.94   6.544%   $252.4454   $252.45   $252.45   $252.40  
  Purchase #3 $201.38   4.721%   $210.8871   $210.89   $210.90   $210.90  
  Purchase #4 $22.90   3.446%   $23.6891   $23.69   $23.70   $23.70  
  Purchase #5 $161.32   9.264%   $176.2647   $176.26   $176.25   $176.30  
  Purchase #6 $59.36   8.434%   $64.3664   $64.37   $64.35   $64.40  
  Purchase #7 $239.58   5.581%   $252.951   $252.95   $252.95   $253.00  
  7 purchase totals = $945.95       $1,007.3729   $1,007.38   $1,007.35   $1,007.50