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 $59.52   3.546%   $61.6306   $61.63   $61.65   $61.60  
  Purchase #2 $226.97   11.273%   $252.5563   $252.56   $252.55   $252.60  
  Purchase #3 $154.27   9.291%   $168.6032   $168.60   $168.60   $168.60  
  Purchase #4 $166.61   12.233%   $186.9914   $186.99   $187.00   $187.00  
  Purchase #5 $193.26   5.167%   $203.2457   $203.25   $203.25   $203.20  
  Purchase #6 $143.45   13.622%   $162.9908   $162.99   $163.00   $163.00  
  Purchase #7 $211.74   11.768%   $236.6576   $236.66   $236.65   $236.70  
  7 purchase totals = $1,155.82       $1,272.6756   $1,272.68   $1,272.70   $1,272.70