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 $53.63   6.848%   $57.3026   $57.30   $57.30   $57.30  
  Purchase #2 $136.37   8.469%   $147.9192   $147.92   $147.90   $147.90  
  Purchase #3 $186.73   11.360%   $207.9425   $207.94   $207.95   $207.90  
  Purchase #4 $96.97   13.444%   $110.0066   $110.01   $110.00   $110.00  
  Purchase #5 $14.95   6.714%   $15.9537   $15.95   $15.95   $16.00  
  Purchase #6 $201.74   10.277%   $222.4728   $222.47   $222.45   $222.50  
  Purchase #7 $193.48   4.754%   $202.678   $202.68   $202.70   $202.70  
  7 purchase totals = $883.87       $964.2754   $964.27   $964.25   $964.30