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 $22.92   3.376%   $23.6938   $23.69   $23.70   $23.70  
  Purchase #2 $57.83   12.572%   $65.1004   $65.10   $65.10   $65.10  
  Purchase #3 $178.39   11.569%   $199.0279   $199.03   $199.05   $199.00  
  Purchase #4 $199.26   4.370%   $207.9677   $207.97   $207.95   $208.00  
  Purchase #5 $177.31   10.811%   $196.479   $196.48   $196.50   $196.50  
  Purchase #6 $144.61   4.447%   $151.0408   $151.04   $151.05   $151.00  
  Purchase #7 $17.93   9.183%   $19.5765   $19.58   $19.60   $19.60  
  7 purchase totals = $798.25       $862.8861   $862.89   $862.95   $862.90