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 $30.51   5.634%   $32.2289   $32.23   $32.25   $32.20  
  Purchase #2 $164.81   7.191%   $176.6615   $176.66   $176.65   $176.70  
  Purchase #3 $221.40   5.345%   $233.2338   $233.23   $233.25   $233.20  
  Purchase #4 $201.57   10.220%   $222.1705   $222.17   $222.15   $222.20  
  Purchase #5 $42.67   11.675%   $47.6517   $47.65   $47.65   $47.70  
  Purchase #6 $186.80   12.857%   $210.8169   $210.82   $210.80   $210.80  
  Purchase #7 $28.92   4.517%   $30.2263   $30.23   $30.25   $30.20  
  7 purchase totals = $876.68       $952.9896   $952.99   $953.00   $953.00