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 $211.97   12.870%   $239.2505   $239.25   $239.25   $239.30  
  Purchase #2 $110.44   8.145%   $119.4353   $119.44   $119.45   $119.40  
  Purchase #3 $176.98   5.404%   $186.544   $186.54   $186.55   $186.50  
  Purchase #4 $192.93   10.789%   $213.7452   $213.75   $213.75   $213.70  
  Purchase #5 $30.57   6.670%   $32.609   $32.61   $32.60   $32.60  
  Purchase #6 $72.45   6.836%   $77.4027   $77.40   $77.40   $77.40  
  Purchase #7 $164.51   4.851%   $172.4904   $172.49   $172.50   $172.50  
  7 purchase totals = $959.85       $1,041.4771   $1,041.48   $1,041.50   $1,041.40