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 $219.96   9.757%   $241.4215   $241.42   $241.40   $241.40  
  Purchase #2 $109.75   8.680%   $119.2763   $119.28   $119.30   $119.30  
  Purchase #3 $237.50   4.436%   $248.0355   $248.04   $248.05   $248.00  
  Purchase #4 $104.48   13.589%   $118.6778   $118.68   $118.70   $118.70  
  Purchase #5 $71.74   3.131%   $73.9862   $73.99   $74.00   $74.00  
  Purchase #6 $209.78   6.233%   $222.8556   $222.86   $222.85   $222.90  
  Purchase #7 $39.85   8.720%   $43.3249   $43.32   $43.30   $43.30  
  7 purchase totals = $993.06       $1,067.5778   $1,067.59   $1,067.60   $1,067.60