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 $239.82   11.271%   $266.8501   $266.85   $266.85   $266.90  
  Purchase #2 $98.96   9.705%   $108.5641   $108.56   $108.55   $108.60  
  Purchase #3 $250.98   3.219%   $259.059   $259.06   $259.05   $259.10  
  Purchase #4 $72.76   8.725%   $79.1083   $79.11   $79.10   $79.10  
  Purchase #5 $54.51   8.569%   $59.181   $59.18   $59.20   $59.20  
  Purchase #6 $40.36   3.866%   $41.9203   $41.92   $41.90   $41.90  
  Purchase #7 $46.30   3.515%   $47.9274   $47.93   $47.95   $47.90  
  7 purchase totals = $803.69       $862.6102   $862.61   $862.60   $862.70