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 $240.53   10.726%   $266.3292   $266.33   $266.35   $266.30  
  Purchase #2 $24.85   7.545%   $26.7249   $26.72   $26.70   $26.70  
  Purchase #3 $51.53   12.192%   $57.8125   $57.81   $57.80   $57.80  
  Purchase #4 $123.92   12.485%   $139.3914   $139.39   $139.40   $139.40  
  Purchase #5 $216.81   10.643%   $239.8851   $239.89   $239.90   $239.90  
  Purchase #6 $27.35   8.626%   $29.7092   $29.71   $29.70   $29.70  
  Purchase #7 $204.28   10.827%   $226.3974   $226.40   $226.40   $226.40  
  7 purchase totals = $889.27       $986.2497   $986.25   $986.25   $986.20