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 $23.42   13.660%   $26.6192   $26.62   $26.60   $26.60  
  Purchase #2 $23.34   5.811%   $24.6963   $24.70   $24.70   $24.70  
  Purchase #3 $13.34   4.250%   $13.907   $13.91   $13.90   $13.90  
  Purchase #4 $193.29   7.836%   $208.4362   $208.44   $208.45   $208.40  
  Purchase #5 $101.88   12.234%   $114.344   $114.34   $114.35   $114.30  
  Purchase #6 $49.73   4.571%   $52.0032   $52.00   $52.00   $52.00  
  Purchase #7 $18.77   6.711%   $20.0297   $20.03   $20.05   $20.00  
  7 purchase totals = $423.77       $460.0356   $460.04   $460.05   $459.90