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 $26.96   9.514%   $29.525   $29.53   $29.55   $29.50  
  Purchase #2 $84.80   12.168%   $95.1185   $95.12   $95.10   $95.10  
  Purchase #3 $93.66   6.423%   $99.6758   $99.68   $99.70   $99.70  
  Purchase #4 $38.63   7.854%   $41.664   $41.66   $41.65   $41.70  
  Purchase #5 $58.34   8.495%   $63.296   $63.30   $63.30   $63.30  
  Purchase #6 $234.68   11.511%   $261.694   $261.69   $261.70   $261.70  
  Purchase #7 $248.49   10.155%   $273.7242   $273.72   $273.70   $273.70  
  7 purchase totals = $785.56       $864.6975   $864.70   $864.70   $864.70