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 $214.81   11.616%   $239.7623   $239.76   $239.75   $239.80  
  Purchase #2 $151.72   3.627%   $157.2229   $157.22   $157.20   $157.20  
  Purchase #3 $74.65   5.756%   $78.9469   $78.95   $78.95   $78.90  
  Purchase #4 $157.85   11.343%   $175.7549   $175.75   $175.75   $175.80  
  Purchase #5 $241.74   9.788%   $265.4015   $265.40   $265.40   $265.40  
  Purchase #6 $80.30   4.396%   $83.83   $83.83   $83.85   $83.80  
  Purchase #7 $27.80   4.358%   $29.0115   $29.01   $29.00   $29.00  
  7 purchase totals = $948.87       $1,029.9300   $1,029.92   $1,029.90   $1,029.90