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 $208.67   13.450%   $236.7361   $236.74   $236.75   $236.70  
  Purchase #2 $16.34   12.615%   $18.4013   $18.40   $18.40   $18.40  
  Purchase #3 $140.66   12.746%   $158.5885   $158.59   $158.60   $158.60  
  Purchase #4 $93.69   12.527%   $105.4265   $105.43   $105.45   $105.40  
  Purchase #5 $165.45   4.686%   $173.203   $173.20   $173.20   $173.20  
  Purchase #6 $80.82   7.698%   $87.0415   $87.04   $87.05   $87.00  
  Purchase #7 $38.53   11.586%   $42.9941   $42.99   $43.00   $43.00  
  7 purchase totals = $744.16       $822.3910   $822.39   $822.45   $822.30