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 $133.79   13.801%   $152.2544   $152.25   $152.25   $152.30  
  Purchase #2 $226.64   11.699%   $253.1546   $253.15   $253.15   $253.20  
  Purchase #3 $118.25   4.270%   $123.2993   $123.30   $123.30   $123.30  
  Purchase #4 $248.63   4.242%   $259.1769   $259.18   $259.20   $259.20  
  Purchase #5 $242.43   10.788%   $268.5833   $268.58   $268.60   $268.60  
  Purchase #6 $86.92   13.273%   $98.4569   $98.46   $98.45   $98.50  
  Purchase #7 $83.51   3.141%   $86.133   $86.13   $86.15   $86.10  
  7 purchase totals = $1,140.17       $1,241.0584   $1,241.05   $1,241.10   $1,241.20