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 $219.45   3.219%   $226.5141   $226.51   $226.50   $226.50  
  Purchase #2 $98.68   4.709%   $103.3268   $103.33   $103.35   $103.30  
  Purchase #3 $167.47   8.715%   $182.065   $182.07   $182.05   $182.10  
  Purchase #4 $114.33   13.381%   $129.6285   $129.63   $129.65   $129.60  
  Purchase #5 $190.53   8.828%   $207.35   $207.35   $207.35   $207.40  
  Purchase #6 $81.61   12.705%   $91.9786   $91.98   $92.00   $92.00  
  Purchase #7 $103.89   9.826%   $114.0982   $114.10   $114.10   $114.10  
  7 purchase totals = $975.96       $1,054.9612   $1,054.97   $1,055.00   $1,055.00