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 $197.83   4.162%   $206.0637   $206.06   $206.05   $206.10  
  Purchase #2 $176.78   3.859%   $183.6019   $183.60   $183.60   $183.60  
  Purchase #3 $40.95   8.704%   $44.5143   $44.51   $44.50   $44.50  
  Purchase #4 $242.33   10.541%   $267.874   $267.87   $267.85   $267.90  
  Purchase #5 $115.29   4.156%   $120.0815   $120.08   $120.10   $120.10  
  Purchase #6 $250.77   3.653%   $259.9306   $259.93   $259.95   $259.90  
  Purchase #7 $141.54   10.749%   $156.7541   $156.75   $156.75   $156.80  
  7 purchase totals = $1,165.49       $1,238.8201   $1,238.80   $1,238.80   $1,238.90