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 $21.95   8.176%   $23.7446   $23.74   $23.75   $23.70  
  Purchase #2 $134.77   13.774%   $153.3332   $153.33   $153.35   $153.30  
  Purchase #3 $248.47   5.706%   $262.6477   $262.65   $262.65   $262.60  
  Purchase #4 $164.82   7.330%   $176.9013   $176.90   $176.90   $176.90  
  Purchase #5 $77.70   4.634%   $81.3006   $81.30   $81.30   $81.30  
  Purchase #6 $71.63   6.808%   $76.5066   $76.51   $76.50   $76.50  
  Purchase #7 $174.95   11.407%   $194.9065   $194.91   $194.90   $194.90  
  7 purchase totals = $894.29       $969.3405   $969.34   $969.35   $969.20