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 $208.62   13.759%   $237.324   $237.32   $237.30   $237.30  
  Purchase #2 $71.73   10.197%   $79.0443   $79.04   $79.05   $79.00  
  Purchase #3 $215.49   9.581%   $236.1361   $236.14   $236.15   $236.10  
  Purchase #4 $87.55   11.585%   $97.6927   $97.69   $97.70   $97.70  
  Purchase #5 $61.59   10.271%   $67.9159   $67.92   $67.90   $67.90  
  Purchase #6 $20.79   6.555%   $22.1528   $22.15   $22.15   $22.20  
  Purchase #7 $161.76   13.861%   $184.1816   $184.18   $184.20   $184.20  
  7 purchase totals = $827.53       $924.4474   $924.44   $924.45   $924.40