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 $14.85   11.765%   $16.5971   $16.60   $16.60   $16.60  
  Purchase #2 $127.57   11.765%   $142.5786   $142.58   $142.60   $142.60  
  Purchase #3 $249.44   4.127%   $259.7344   $259.73   $259.75   $259.70  
  Purchase #4 $18.63   6.177%   $19.7808   $19.78   $19.80   $19.80  
  Purchase #5 $178.92   10.370%   $197.474   $197.47   $197.45   $197.50  
  Purchase #6 $132.33   3.508%   $136.9721   $136.97   $136.95   $137.00  
  Purchase #7 $208.49   6.619%   $222.29   $222.29   $222.30   $222.30  
  7 purchase totals = $930.23       $995.4270   $995.42   $995.45   $995.50