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 $152.65   6.509%   $162.586   $162.59   $162.60   $162.60  
  Purchase #2 $5.74   3.733%   $5.9543   $5.95   $5.95   $6.00  
  Purchase #3 $200.42   4.509%   $209.4569   $209.46   $209.45   $209.50  
  Purchase #4 $47.83   4.443%   $49.9551   $49.96   $49.95   $50.00  
  Purchase #5 $208.78   11.615%   $233.0298   $233.03   $233.05   $233.00  
  Purchase #6 $235.28   3.599%   $243.7477   $243.75   $243.75   $243.70  
  Purchase #7 $236.58   6.809%   $252.6887   $252.69   $252.70   $252.70  
  7 purchase totals = $1,087.28       $1,157.4185   $1,157.43   $1,157.45   $1,157.50