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 $233.76   7.723%   $251.8133   $251.81   $251.80   $251.80  
  Purchase #2 $53.68   7.314%   $57.6062   $57.61   $57.60   $57.60  
  Purchase #3 $60.49   5.861%   $64.0353   $64.04   $64.05   $64.00  
  Purchase #4 $207.31   3.365%   $214.286   $214.29   $214.30   $214.30  
  Purchase #5 $103.47   10.539%   $114.3747   $114.37   $114.35   $114.40  
  Purchase #6 $104.54   3.339%   $108.0306   $108.03   $108.05   $108.00  
  Purchase #7 $233.26   11.154%   $259.2778   $259.28   $259.30   $259.30  
  7 purchase totals = $996.51       $1,069.4239   $1,069.43   $1,069.45   $1,069.40