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 $248.35   10.743%   $275.0302   $275.03   $275.05   $275.00  
  Purchase #2 $190.75   12.142%   $213.9109   $213.91   $213.90   $213.90  
  Purchase #3 $243.30   6.275%   $258.5671   $258.57   $258.55   $258.60  
  Purchase #4 $183.96   3.705%   $190.7757   $190.78   $190.80   $190.80  
  Purchase #5 $106.72   7.559%   $114.787   $114.79   $114.80   $114.80  
  Purchase #6 $188.39   10.863%   $208.8548   $208.85   $208.85   $208.90  
  Purchase #7 $240.50   8.614%   $261.2167   $261.22   $261.20   $261.20  
  7 purchase totals = $1,401.97       $1,523.1424   $1,523.15   $1,523.15   $1,523.20