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 $66.93   10.613%   $74.0333   $74.03   $74.05   $74.00  
  Purchase #2 $241.41   7.669%   $259.9237   $259.92   $259.90   $259.90  
  Purchase #3 $177.81   8.113%   $192.2357   $192.24   $192.25   $192.20  
  Purchase #4 $43.97   8.437%   $47.6797   $47.68   $47.70   $47.70  
  Purchase #5 $208.39   9.453%   $228.0891   $228.09   $228.10   $228.10  
  Purchase #6 $23.69   10.818%   $26.2528   $26.25   $26.25   $26.30  
  Purchase #7 $194.43   3.152%   $200.5584   $200.56   $200.55   $200.60  
  7 purchase totals = $956.63       $1,028.7727   $1,028.77   $1,028.80   $1,028.80