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 $239.44   11.208%   $266.2764   $266.28   $266.30   $266.30  
  Purchase #2 $43.55   8.815%   $47.3889   $47.39   $47.40   $47.40  
  Purchase #3 $161.53   11.167%   $179.5681   $179.57   $179.55   $179.60  
  Purchase #4 $152.66   12.137%   $171.1883   $171.19   $171.20   $171.20  
  Purchase #5 $32.72   5.608%   $34.5549   $34.55   $34.55   $34.60  
  Purchase #6 $114.59   8.436%   $124.2568   $124.26   $124.25   $124.30  
  Purchase #7 $19.81   11.483%   $22.0848   $22.08   $22.10   $22.10  
  7 purchase totals = $764.30       $845.3182   $845.32   $845.35   $845.50