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 $244.32   8.584%   $265.2924   $265.29   $265.30   $265.30  
  Purchase #2 $165.75   13.114%   $187.4865   $187.49   $187.50   $187.50  
  Purchase #3 $230.39   11.153%   $256.0854   $256.09   $256.10   $256.10  
  Purchase #4 $222.64   7.597%   $239.554   $239.55   $239.55   $239.60  
  Purchase #5 $94.80   3.544%   $98.1597   $98.16   $98.15   $98.20  
  Purchase #6 $28.89   4.706%   $30.2496   $30.25   $30.25   $30.20  
  Purchase #7 $207.37   13.212%   $234.7677   $234.77   $234.75   $234.80  
  7 purchase totals = $1,194.16       $1,311.5953   $1,311.60   $1,311.60   $1,311.70