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 $236.37   10.671%   $261.593   $261.59   $261.60   $261.60  
  Purchase #2 $222.45   12.807%   $250.9392   $250.94   $250.95   $250.90  
  Purchase #3 $71.61   4.820%   $75.0616   $75.06   $75.05   $75.10  
  Purchase #4 $48.84   6.466%   $51.998   $52.00   $52.00   $52.00  
  Purchase #5 $197.42   5.497%   $208.2722   $208.27   $208.25   $208.30  
  Purchase #6 $97.45   8.290%   $105.5286   $105.53   $105.55   $105.50  
  Purchase #7 $88.68   11.262%   $98.6671   $98.67   $98.65   $98.70  
  7 purchase totals = $962.82       $1,052.0597   $1,052.06   $1,052.05   $1,052.10