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 $224.63   12.303%   $252.2662   $252.27   $252.25   $252.30  
  Purchase #2 $101.50   12.326%   $114.0109   $114.01   $114.00   $114.00  
  Purchase #3 $55.71   4.287%   $58.0983   $58.10   $58.10   $58.10  
  Purchase #4 $101.86   13.743%   $115.8586   $115.86   $115.85   $115.90  
  Purchase #5 $237.25   4.508%   $247.9452   $247.95   $247.95   $247.90  
  Purchase #6 $78.59   10.402%   $86.7649   $86.76   $86.75   $86.80  
  Purchase #7 $111.43   10.834%   $123.5023   $123.50   $123.50   $123.50  
  7 purchase totals = $910.97       $998.4464   $998.45   $998.40   $998.50