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 $56.28   9.517%   $61.6362   $61.64   $61.65   $61.60  
  Purchase #2 $50.93   5.493%   $53.7276   $53.73   $53.75   $53.70  
  Purchase #3 $89.41   4.452%   $93.3905   $93.39   $93.40   $93.40  
  Purchase #4 $197.73   5.303%   $208.2156   $208.22   $208.20   $208.20  
  Purchase #5 $33.47   9.286%   $36.578   $36.58   $36.60   $36.60  
  Purchase #6 $14.36   13.142%   $16.2472   $16.25   $16.25   $16.20  
  Purchase #7 $230.73   13.538%   $261.9662   $261.97   $261.95   $262.00  
  7 purchase totals = $672.91       $731.7613   $731.78   $731.80   $731.70