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 $130.29   7.393%   $139.9223   $139.92   $139.90   $139.90  
  Purchase #2 $122.41   12.262%   $137.4199   $137.42   $137.40   $137.40  
  Purchase #3 $174.26   6.510%   $185.6043   $185.60   $185.60   $185.60  
  Purchase #4 $101.78   13.338%   $115.3554   $115.36   $115.35   $115.40  
  Purchase #5 $231.63   9.260%   $253.0789   $253.08   $253.10   $253.10  
  Purchase #6 $215.71   7.470%   $231.8235   $231.82   $231.80   $231.80  
  Purchase #7 $78.54   10.271%   $86.6068   $86.61   $86.60   $86.60  
  7 purchase totals = $1,054.62       $1,149.8111   $1,149.81   $1,149.75   $1,149.80