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 $207.85   13.643%   $236.207   $236.21   $236.20   $236.20  
  Purchase #2 $78.83   6.641%   $84.0651   $84.07   $84.05   $84.10  
  Purchase #3 $35.79   3.200%   $36.9353   $36.94   $36.95   $36.90  
  Purchase #4 $53.65   12.117%   $60.1508   $60.15   $60.15   $60.20  
  Purchase #5 $105.76   7.521%   $113.7142   $113.71   $113.70   $113.70  
  Purchase #6 $70.50   8.686%   $76.6236   $76.62   $76.60   $76.60  
  Purchase #7 $106.83   8.727%   $116.1531   $116.15   $116.15   $116.20  
  7 purchase totals = $659.21       $723.8491   $723.85   $723.80   $723.90