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 $203.94   12.396%   $229.2204   $229.22   $229.20   $229.20  
  Purchase #2 $152.96   11.827%   $171.0506   $171.05   $171.05   $171.10  
  Purchase #3 $124.80   7.473%   $134.1263   $134.13   $134.15   $134.10  
  Purchase #4 $186.91   11.608%   $208.6065   $208.61   $208.60   $208.60  
  Purchase #5 $163.99   6.837%   $175.202   $175.20   $175.20   $175.20  
  Purchase #6 $73.31   6.757%   $78.2636   $78.26   $78.25   $78.30  
  Purchase #7 $170.47   9.847%   $187.2562   $187.26   $187.25   $187.30  
  7 purchase totals = $1,076.38       $1,183.7256   $1,183.73   $1,183.70   $1,183.80