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 $232.39   12.639%   $261.7618   $261.76   $261.75   $261.80  
  Purchase #2 $164.78   7.417%   $177.0017   $177.00   $177.00   $177.00  
  Purchase #3 $104.93   4.697%   $109.8586   $109.86   $109.85   $109.90  
  Purchase #4 $163.27   12.689%   $183.9873   $183.99   $184.00   $184.00  
  Purchase #5 $222.59   8.670%   $241.8886   $241.89   $241.90   $241.90  
  Purchase #6 $233.26   8.166%   $252.308   $252.31   $252.30   $252.30  
  Purchase #7 $189.81   13.621%   $215.664   $215.66   $215.65   $215.70  
  7 purchase totals = $1,311.03       $1,442.4700   $1,442.47   $1,442.45   $1,442.60