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 $8.42   3.479%   $8.7129   $8.71   $8.70   $8.70  
  Purchase #2 $163.99   13.624%   $186.332   $186.33   $186.35   $186.30  
  Purchase #3 $109.44   4.389%   $114.2433   $114.24   $114.25   $114.20  
  Purchase #4 $8.59   8.505%   $9.3206   $9.32   $9.30   $9.30  
  Purchase #5 $225.99   10.747%   $250.2771   $250.28   $250.30   $250.30  
  Purchase #6 $129.76   13.691%   $147.5254   $147.53   $147.55   $147.50  
  Purchase #7 $9.80   8.669%   $10.6496   $10.65   $10.65   $10.60  
  7 purchase totals = $655.99       $727.0609   $727.06   $727.10   $726.90