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 $92.81   3.442%   $96.0045   $96.00   $96.00   $96.00  
  Purchase #2 $19.68   4.858%   $20.6361   $20.64   $20.65   $20.60  
  Purchase #3 $245.27   6.143%   $260.3369   $260.34   $260.35   $260.30  
  Purchase #4 $146.75   7.230%   $157.36   $157.36   $157.35   $157.40  
  Purchase #5 $74.66   5.316%   $78.6289   $78.63   $78.65   $78.60  
  Purchase #6 $207.93   13.327%   $235.6408   $235.64   $235.65   $235.60  
  Purchase #7 $65.70   7.238%   $70.4554   $70.46   $70.45   $70.50  
  7 purchase totals = $852.80       $919.0626   $919.07   $919.10   $919.00