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 $43.84   11.741%   $48.9873   $48.99   $49.00   $49.00  
  Purchase #2 $236.30   6.623%   $251.9501   $251.95   $251.95   $252.00  
  Purchase #3 $108.77   5.133%   $114.3532   $114.35   $114.35   $114.40  
  Purchase #4 $139.76   9.161%   $152.5634   $152.56   $152.55   $152.60  
  Purchase #5 $74.99   10.314%   $82.7245   $82.72   $82.70   $82.70  
  Purchase #6 $176.76   9.810%   $194.1002   $194.10   $194.10   $194.10  
  Purchase #7 $154.39   11.509%   $172.1587   $172.16   $172.15   $172.20  
  7 purchase totals = $934.81       $1,016.8374   $1,016.83   $1,016.80   $1,017.00