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 $73.90   3.522%   $76.5028   $76.50   $76.50   $76.50  
  Purchase #2 $236.26   12.334%   $265.4003   $265.40   $265.40   $265.40  
  Purchase #3 $10.54   3.626%   $10.9222   $10.92   $10.90   $10.90  
  Purchase #4 $103.72   11.528%   $115.6768   $115.68   $115.70   $115.70  
  Purchase #5 $165.89   5.771%   $175.4635   $175.46   $175.45   $175.50  
  Purchase #6 $83.61   3.848%   $86.8273   $86.83   $86.85   $86.80  
  Purchase #7 $217.86   5.197%   $229.1822   $229.18   $229.20   $229.20  
  7 purchase totals = $891.78       $959.9751   $959.97   $960.00   $960.00