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 $114.50   3.109%   $118.0598   $118.06   $118.05   $118.10  
  Purchase #2 $11.38   8.232%   $12.3168   $12.32   $12.30   $12.30  
  Purchase #3 $200.45   13.710%   $227.9317   $227.93   $227.95   $227.90  
  Purchase #4 $164.36   12.546%   $184.9806   $184.98   $185.00   $185.00  
  Purchase #5 $212.67   13.134%   $240.6021   $240.60   $240.60   $240.60  
  Purchase #6 $191.62   8.547%   $207.9978   $208.00   $208.00   $208.00  
  Purchase #7 $212.61   12.693%   $239.5966   $239.60   $239.60   $239.60  
  7 purchase totals = $1,107.59       $1,231.4854   $1,231.49   $1,231.50   $1,231.50