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 $93.48   4.859%   $98.0222   $98.02   $98.00   $98.00  
  Purchase #2 $137.41   11.347%   $153.0019   $153.00   $153.00   $153.00  
  Purchase #3 $69.40   6.852%   $74.1553   $74.16   $74.15   $74.20  
  Purchase #4 $74.77   5.312%   $78.7418   $78.74   $78.75   $78.70  
  Purchase #5 $182.64   3.176%   $188.4406   $188.44   $188.45   $188.40  
  Purchase #6 $137.86   7.542%   $148.2574   $148.26   $148.25   $148.30  
  Purchase #7 $180.44   5.346%   $190.0863   $190.09   $190.10   $190.10  
  7 purchase totals = $876.00       $930.7055   $930.71   $930.70   $930.70