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 $177.64   11.228%   $197.5854   $197.59   $197.60   $197.60  
  Purchase #2 $89.99   12.771%   $101.4826   $101.48   $101.50   $101.50  
  Purchase #3 $48.47   8.492%   $52.5861   $52.59   $52.60   $52.60  
  Purchase #4 $249.72   9.520%   $273.4933   $273.49   $273.50   $273.50  
  Purchase #5 $247.41   5.695%   $261.5   $261.50   $261.50   $261.50  
  Purchase #6 $95.49   5.566%   $100.805   $100.81   $100.80   $100.80  
  Purchase #7 $81.77   11.310%   $91.0182   $91.02   $91.00   $91.00  
  7 purchase totals = $990.49       $1,078.4706   $1,078.48   $1,078.50   $1,078.50