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 $56.69   13.864%   $64.5495   $64.55   $64.55   $64.50  
  Purchase #2 $23.38   3.742%   $24.2549   $24.25   $24.25   $24.30  
  Purchase #3 $13.89   13.734%   $15.7977   $15.80   $15.80   $15.80  
  Purchase #4 $71.59   8.716%   $77.8298   $77.83   $77.85   $77.80  
  Purchase #5 $217.73   3.146%   $224.5798   $224.58   $224.60   $224.60  
  Purchase #6 $79.30   9.453%   $86.7962   $86.80   $86.80   $86.80  
  Purchase #7 $231.33   3.599%   $239.6556   $239.66   $239.65   $239.70  
  7 purchase totals = $693.91       $733.4635   $733.47   $733.50   $733.50