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 $24.36   8.807%   $26.5054   $26.51   $26.50   $26.50  
  Purchase #2 $239.43   4.481%   $250.1589   $250.16   $250.15   $250.20  
  Purchase #3 $146.57   10.602%   $162.1094   $162.11   $162.10   $162.10  
  Purchase #4 $124.91   13.734%   $142.0651   $142.07   $142.05   $142.10  
  Purchase #5 $69.85   7.423%   $75.035   $75.04   $75.05   $75.00  
  Purchase #6 $61.82   5.127%   $64.9895   $64.99   $65.00   $65.00  
  Purchase #7 $162.74   12.514%   $183.1053   $183.11   $183.10   $183.10  
  7 purchase totals = $829.68       $903.9686   $903.99   $903.95   $904.00