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 $213.90   10.658%   $236.6975   $236.70   $236.70   $236.70  
  Purchase #2 $167.45   3.177%   $172.7699   $172.77   $172.75   $172.80  
  Purchase #3 $185.27   4.545%   $193.6905   $193.69   $193.70   $193.70  
  Purchase #4 $80.88   10.856%   $89.6603   $89.66   $89.65   $89.70  
  Purchase #5 $58.93   11.863%   $65.9209   $65.92   $65.90   $65.90  
  Purchase #6 $162.70   8.588%   $176.6727   $176.67   $176.65   $176.70  
  Purchase #7 $22.69   4.629%   $23.7403   $23.74   $23.75   $23.70  
  7 purchase totals = $891.82       $959.1521   $959.15   $959.10   $959.20