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 $22.36   8.673%   $24.2993   $24.30   $24.30   $24.30  
  Purchase #2 $110.67   10.266%   $122.0314   $122.03   $122.05   $122.00  
  Purchase #3 $56.76   6.779%   $60.6078   $60.61   $60.60   $60.60  
  Purchase #4 $213.92   8.326%   $231.731   $231.73   $231.75   $231.70  
  Purchase #5 $192.47   5.246%   $202.567   $202.57   $202.55   $202.60  
  Purchase #6 $176.38   5.856%   $186.7088   $186.71   $186.70   $186.70  
  Purchase #7 $48.53   12.585%   $54.6375   $54.64   $54.65   $54.60  
  7 purchase totals = $821.09       $882.5828   $882.59   $882.60   $882.50