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 $38.48   13.382%   $43.6294   $43.63   $43.65   $43.60  
  Purchase #2 $242.34   13.372%   $274.7457   $274.75   $274.75   $274.70  
  Purchase #3 $84.90   9.503%   $92.968   $92.97   $92.95   $93.00  
  Purchase #4 $56.49   7.500%   $60.7268   $60.73   $60.75   $60.70  
  Purchase #5 $201.82   12.670%   $227.3906   $227.39   $227.40   $227.40  
  Purchase #6 $246.90   4.599%   $258.2549   $258.25   $258.25   $258.30  
  Purchase #7 $196.89   8.766%   $214.1494   $214.15   $214.15   $214.10  
  7 purchase totals = $1,067.82       $1,171.8648   $1,171.87   $1,171.90   $1,171.80