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 $23.46   12.874%   $26.4802   $26.48   $26.50   $26.50  
  Purchase #2 $227.83   13.622%   $258.865   $258.87   $258.85   $258.90  
  Purchase #3 $109.88   8.609%   $119.3396   $119.34   $119.35   $119.30  
  Purchase #4 $158.44   9.727%   $173.8515   $173.85   $173.85   $173.90  
  Purchase #5 $245.88   5.672%   $259.8263   $259.83   $259.85   $259.80  
  Purchase #6 $239.41   12.549%   $269.4536   $269.45   $269.45   $269.50  
  Purchase #7 $173.60   11.691%   $193.8956   $193.90   $193.90   $193.90  
  7 purchase totals = $1,178.50       $1,301.7118   $1,301.72   $1,301.75   $1,301.80