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 $241.25   8.141%   $260.8902   $260.89   $260.90   $260.90  
  Purchase #2 $10.94   3.774%   $11.3529   $11.35   $11.35   $11.40  
  Purchase #3 $139.55   8.451%   $151.3434   $151.34   $151.35   $151.30  
  Purchase #4 $231.57   12.783%   $261.1716   $261.17   $261.15   $261.20  
  Purchase #5 $44.63   9.404%   $48.827   $48.83   $48.85   $48.80  
  Purchase #6 $245.25   9.740%   $269.1374   $269.14   $269.15   $269.10  
  Purchase #7 $58.47   4.408%   $61.0474   $61.05   $61.05   $61.00  
  7 purchase totals = $971.66       $1,063.7699   $1,063.77   $1,063.80   $1,063.70