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 $156.87   13.634%   $178.2577   $178.26   $178.25   $178.30  
  Purchase #2 $7.83   7.234%   $8.3964   $8.40   $8.40   $8.40  
  Purchase #3 $164.91   3.723%   $171.0496   $171.05   $171.05   $171.00  
  Purchase #4 $216.81   11.244%   $241.1881   $241.19   $241.20   $241.20  
  Purchase #5 $77.69   5.551%   $82.0026   $82.00   $82.00   $82.00  
  Purchase #6 $240.88   3.246%   $248.699   $248.70   $248.70   $248.70  
  Purchase #7 $114.68   7.213%   $122.9519   $122.95   $122.95   $123.00  
  7 purchase totals = $979.67       $1,052.5453   $1,052.55   $1,052.55   $1,052.60