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 $183.64   13.788%   $208.9603   $208.96   $208.95   $209.00  
  Purchase #2 $8.81   7.297%   $9.4529   $9.45   $9.45   $9.50  
  Purchase #3 $202.50   13.525%   $229.8881   $229.89   $229.90   $229.90  
  Purchase #4 $141.99   3.591%   $147.0889   $147.09   $147.10   $147.10  
  Purchase #5 $110.58   4.688%   $115.764   $115.76   $115.75   $115.80  
  Purchase #6 $196.28   9.870%   $215.6528   $215.65   $215.65   $215.70  
  Purchase #7 $197.26   8.686%   $214.394   $214.39   $214.40   $214.40  
  7 purchase totals = $1,041.06       $1,141.2010   $1,141.19   $1,141.20   $1,141.40