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 $229.51   13.775%   $261.125   $261.13   $261.15   $261.10  
  Purchase #2 $158.54   13.268%   $179.5751   $179.58   $179.60   $179.60  
  Purchase #3 $77.41   5.501%   $81.6683   $81.67   $81.65   $81.70  
  Purchase #4 $48.36   7.298%   $51.8893   $51.89   $51.90   $51.90  
  Purchase #5 $122.33   3.157%   $126.192   $126.19   $126.20   $126.20  
  Purchase #6 $92.80   8.195%   $100.405   $100.41   $100.40   $100.40  
  Purchase #7 $149.28   9.599%   $163.6094   $163.61   $163.60   $163.60  
  7 purchase totals = $878.23       $964.4641   $964.48   $964.50   $964.50