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 $119.76   6.254%   $127.2498   $127.25   $127.25   $127.20  
  Purchase #2 $73.39   6.550%   $78.197   $78.20   $78.20   $78.20  
  Purchase #3 $89.39   4.174%   $93.1211   $93.12   $93.10   $93.10  
  Purchase #4 $79.99   13.277%   $90.6103   $90.61   $90.60   $90.60  
  Purchase #5 $213.68   7.131%   $228.9175   $228.92   $228.90   $228.90  
  Purchase #6 $94.86   10.678%   $104.9892   $104.99   $105.00   $105.00  
  Purchase #7 $247.97   8.175%   $268.2415   $268.24   $268.25   $268.20  
  7 purchase totals = $919.04       $991.3264   $991.33   $991.30   $991.20