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 $239.97   9.438%   $262.6184   $262.62   $262.60   $262.60  
  Purchase #2 $211.97   8.366%   $229.7034   $229.70   $229.70   $229.70  
  Purchase #3 $24.36   8.495%   $26.4294   $26.43   $26.45   $26.40  
  Purchase #4 $73.81   3.703%   $76.5432   $76.54   $76.55   $76.50  
  Purchase #5 $82.99   11.253%   $92.3289   $92.33   $92.35   $92.30  
  Purchase #6 $23.49   8.457%   $25.4765   $25.48   $25.50   $25.50  
  Purchase #7 $244.26   12.287%   $274.2722   $274.27   $274.25   $274.30  
  7 purchase totals = $900.85       $987.3720   $987.37   $987.40   $987.30