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 $114.44   4.288%   $119.3472   $119.35   $119.35   $119.30  
  Purchase #2 $222.69   6.250%   $236.6081   $236.61   $236.60   $236.60  
  Purchase #3 $247.34   5.613%   $261.2232   $261.22   $261.20   $261.20  
  Purchase #4 $159.56   10.460%   $176.25   $176.25   $176.25   $176.30  
  Purchase #5 $173.49   10.276%   $191.3178   $191.32   $191.30   $191.30  
  Purchase #6 $131.83   7.239%   $141.3732   $141.37   $141.35   $141.40  
  Purchase #7 $209.72   12.192%   $235.2891   $235.29   $235.30   $235.30  
  7 purchase totals = $1,259.07       $1,361.4086   $1,361.41   $1,361.35   $1,361.40