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 $60.44   13.198%   $68.4169   $68.42   $68.40   $68.40  
  Purchase #2 $125.44   9.805%   $137.7394   $137.74   $137.75   $137.70  
  Purchase #3 $186.88   11.756%   $208.8496   $208.85   $208.85   $208.80  
  Purchase #4 $189.51   9.602%   $207.7068   $207.71   $207.70   $207.70  
  Purchase #5 $6.99   9.328%   $7.642   $7.64   $7.65   $7.60  
  Purchase #6 $168.60   4.769%   $176.6405   $176.64   $176.65   $176.60  
  Purchase #7 $228.63   10.264%   $252.0966   $252.10   $252.10   $252.10  
  7 purchase totals = $966.49       $1,059.0918   $1,059.10   $1,059.10   $1,058.90