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 $195.92   12.767%   $220.9331   $220.93   $220.95   $220.90  
  Purchase #2 $65.76   5.238%   $69.2045   $69.20   $69.20   $69.20  
  Purchase #3 $176.77   3.523%   $182.9976   $183.00   $183.00   $183.00  
  Purchase #4 $204.93   8.409%   $222.1626   $222.16   $222.15   $222.20  
  Purchase #5 $111.31   10.147%   $122.6046   $122.60   $122.60   $122.60  
  Purchase #6 $220.65   13.486%   $250.4069   $250.41   $250.40   $250.40  
  Purchase #7 $174.48   10.441%   $192.6975   $192.70   $192.70   $192.70  
  7 purchase totals = $1,149.82       $1,261.0068   $1,261.00   $1,261.00   $1,261.00