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 $34.71   11.175%   $38.5888   $38.59   $38.60   $38.60  
  Purchase #2 $93.92   10.329%   $103.621   $103.62   $103.60   $103.60  
  Purchase #3 $57.83   10.209%   $63.7339   $63.73   $63.75   $63.70  
  Purchase #4 $177.45   8.566%   $192.6504   $192.65   $192.65   $192.70  
  Purchase #5 $90.63   5.577%   $95.6844   $95.68   $95.70   $95.70  
  Purchase #6 $75.41   6.513%   $80.3215   $80.32   $80.30   $80.30  
  Purchase #7 $135.44   4.872%   $142.0386   $142.04   $142.05   $142.00  
  7 purchase totals = $665.39       $716.6386   $716.63   $716.65   $716.60