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 $183.62   13.326%   $208.0892   $208.09   $208.10   $208.10  
  Purchase #2 $67.72   8.271%   $73.3211   $73.32   $73.30   $73.30  
  Purchase #3 $226.52   5.597%   $239.1983   $239.20   $239.20   $239.20  
  Purchase #4 $162.31   12.372%   $182.391   $182.39   $182.40   $182.40  
  Purchase #5 $73.75   3.318%   $76.197   $76.20   $76.20   $76.20  
  Purchase #6 $221.61   6.333%   $235.6446   $235.64   $235.65   $235.60  
  Purchase #7 $140.48   11.210%   $156.2278   $156.23   $156.25   $156.20  
  7 purchase totals = $1,076.01       $1,171.0690   $1,171.07   $1,171.10   $1,171.00