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 $221.77   11.851%   $248.052   $248.05   $248.05   $248.10  
  Purchase #2 $114.65   10.822%   $127.0574   $127.06   $127.05   $127.10  
  Purchase #3 $227.37   6.787%   $242.8016   $242.80   $242.80   $242.80  
  Purchase #4 $193.86   11.807%   $216.7491   $216.75   $216.75   $216.70  
  Purchase #5 $164.69   4.268%   $171.719   $171.72   $171.70   $171.70  
  Purchase #6 $186.44   3.574%   $193.1034   $193.10   $193.10   $193.10  
  Purchase #7 $74.95   10.712%   $82.9786   $82.98   $83.00   $83.00  
  7 purchase totals = $1,183.73       $1,282.4611   $1,282.46   $1,282.45   $1,282.50