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 $248.58   3.615%   $257.5662   $257.57   $257.55   $257.60  
  Purchase #2 $205.39   5.311%   $216.2983   $216.30   $216.30   $216.30  
  Purchase #3 $67.40   11.335%   $75.0398   $75.04   $75.05   $75.00  
  Purchase #4 $164.84   8.675%   $179.1399   $179.14   $179.15   $179.10  
  Purchase #5 $168.54   5.416%   $177.6681   $177.67   $177.65   $177.70  
  Purchase #6 $60.98   3.131%   $62.8893   $62.89   $62.90   $62.90  
  Purchase #7 $87.77   12.292%   $98.5587   $98.56   $98.55   $98.60  
  7 purchase totals = $1,003.50       $1,067.1603   $1,067.17   $1,067.15   $1,067.20