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 $191.85   12.652%   $216.1229   $216.12   $216.10   $216.10  
  Purchase #2 $101.26   13.233%   $114.6597   $114.66   $114.65   $114.70  
  Purchase #3 $86.67   13.381%   $98.2673   $98.27   $98.25   $98.30  
  Purchase #4 $176.27   9.496%   $193.0086   $193.01   $193.00   $193.00  
  Purchase #5 $157.49   9.149%   $171.8988   $171.90   $171.90   $171.90  
  Purchase #6 $52.59   9.393%   $57.5298   $57.53   $57.55   $57.50  
  Purchase #7 $125.58   5.868%   $132.949   $132.95   $132.95   $132.90  
  7 purchase totals = $891.71       $984.4361   $984.44   $984.40   $984.40