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 $56.85   4.116%   $59.1899   $59.19   $59.20   $59.20  
  Purchase #2 $26.84   7.483%   $28.8484   $28.85   $28.85   $28.80  
  Purchase #3 $102.62   3.689%   $106.4057   $106.41   $106.40   $106.40  
  Purchase #4 $38.42   9.334%   $42.0061   $42.01   $42.00   $42.00  
  Purchase #5 $125.76   6.527%   $133.9684   $133.97   $133.95   $134.00  
  Purchase #6 $230.88   13.248%   $261.467   $261.47   $261.45   $261.50  
  Purchase #7 $117.34   7.493%   $126.1323   $126.13   $126.15   $126.10  
  7 purchase totals = $698.71       $758.0178   $758.03   $758.00   $758.00