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 $222.32   9.147%   $242.6556   $242.66   $242.65   $242.70  
  Purchase #2 $162.67   4.247%   $169.5786   $169.58   $169.60   $169.60  
  Purchase #3 $158.68   13.538%   $180.1621   $180.16   $180.15   $180.20  
  Purchase #4 $214.58   5.108%   $225.5407   $225.54   $225.55   $225.50  
  Purchase #5 $213.48   6.192%   $226.6987   $226.70   $226.70   $226.70  
  Purchase #6 $236.56   11.358%   $263.4285   $263.43   $263.45   $263.40  
  Purchase #7 $60.81   3.861%   $63.1579   $63.16   $63.15   $63.20  
  7 purchase totals = $1,269.10       $1,371.2221   $1,371.23   $1,371.25   $1,371.30