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 $183.26   13.636%   $208.2493   $208.25   $208.25   $208.20  
  Purchase #2 $68.26   6.807%   $72.9065   $72.91   $72.90   $72.90  
  Purchase #3 $192.64   6.548%   $205.2541   $205.25   $205.25   $205.30  
  Purchase #4 $218.45   3.615%   $226.347   $226.35   $226.35   $226.30  
  Purchase #5 $193.77   11.554%   $216.1582   $216.16   $216.15   $216.20  
  Purchase #6 $202.79   13.779%   $230.7324   $230.73   $230.75   $230.70  
  Purchase #7 $114.91   3.277%   $118.6756   $118.68   $118.70   $118.70  
  7 purchase totals = $1,174.08       $1,278.3231   $1,278.33   $1,278.35   $1,278.30