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 $182.66   9.818%   $200.5936   $200.59   $200.60   $200.60  
  Purchase #2 $222.97   7.612%   $239.9425   $239.94   $239.95   $239.90  
  Purchase #3 $115.84   9.865%   $127.2676   $127.27   $127.25   $127.30  
  Purchase #4 $174.69   8.827%   $190.1099   $190.11   $190.10   $190.10  
  Purchase #5 $162.62   9.209%   $177.5957   $177.60   $177.60   $177.60  
  Purchase #6 $68.28   10.599%   $75.517   $75.52   $75.50   $75.50  
  Purchase #7 $189.71   4.102%   $197.4919   $197.49   $197.50   $197.50  
  7 purchase totals = $1,116.77       $1,208.5182   $1,208.52   $1,208.50   $1,208.50