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 $214.50   8.872%   $233.5304   $233.53   $233.55   $233.50  
  Purchase #2 $66.87   10.581%   $73.9455   $73.95   $73.95   $73.90  
  Purchase #3 $54.68   4.735%   $57.2691   $57.27   $57.25   $57.30  
  Purchase #4 $174.85   10.324%   $192.9015   $192.90   $192.90   $192.90  
  Purchase #5 $75.34   9.570%   $82.55   $82.55   $82.55   $82.60  
  Purchase #6 $196.64   7.329%   $211.0517   $211.05   $211.05   $211.10  
  Purchase #7 $15.77   6.570%   $16.8061   $16.81   $16.80   $16.80  
  7 purchase totals = $798.65       $868.0543   $868.06   $868.05   $868.10