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 $84.91   13.423%   $96.3075   $96.31   $96.30   $96.30  
  Purchase #2 $123.65   7.652%   $133.1117   $133.11   $133.10   $133.10  
  Purchase #3 $150.26   8.856%   $163.567   $163.57   $163.55   $163.60  
  Purchase #4 $191.96   5.125%   $201.798   $201.80   $201.80   $201.80  
  Purchase #5 $104.27   9.583%   $114.2622   $114.26   $114.25   $114.30  
  Purchase #6 $108.71   4.862%   $113.9955   $114.00   $114.00   $114.00  
  Purchase #7 $240.94   5.397%   $253.9435   $253.94   $253.95   $253.90  
  7 purchase totals = $1,004.70       $1,076.9854   $1,076.99   $1,076.95   $1,077.00