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 $34.51   11.406%   $38.4462   $38.45   $38.45   $38.40  
  Purchase #2 $162.35   7.767%   $174.9597   $174.96   $174.95   $175.00  
  Purchase #3 $6.71   12.624%   $7.5571   $7.56   $7.55   $7.60  
  Purchase #4 $196.83   5.694%   $208.0375   $208.04   $208.05   $208.00  
  Purchase #5 $128.64   11.210%   $143.0605   $143.06   $143.05   $143.10  
  Purchase #6 $69.97   10.631%   $77.4085   $77.41   $77.40   $77.40  
  Purchase #7 $105.50   8.156%   $114.1046   $114.10   $114.10   $114.10  
  7 purchase totals = $704.51       $763.5741   $763.58   $763.55   $763.60