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 $58.99   3.486%   $61.0464   $61.05   $61.05   $61.00  
  Purchase #2 $154.73   6.382%   $164.6049   $164.60   $164.60   $164.60  
  Purchase #3 $42.81   13.436%   $48.562   $48.56   $48.55   $48.60  
  Purchase #4 $156.28   4.556%   $163.4001   $163.40   $163.40   $163.40  
  Purchase #5 $29.51   5.485%   $31.1286   $31.13   $31.15   $31.10  
  Purchase #6 $67.69   4.822%   $70.954   $70.95   $70.95   $71.00  
  Purchase #7 $176.62   11.524%   $196.9737   $196.97   $196.95   $197.00  
  7 purchase totals = $686.63       $736.6697   $736.66   $736.65   $736.70