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 $197.86   8.613%   $214.9017   $214.90   $214.90   $214.90  
  Purchase #2 $227.89   13.773%   $259.2773   $259.28   $259.30   $259.30  
  Purchase #3 $92.27   8.652%   $100.2532   $100.25   $100.25   $100.30  
  Purchase #4 $47.47   5.125%   $49.9028   $49.90   $49.90   $49.90  
  Purchase #5 $244.27   6.869%   $261.0489   $261.05   $261.05   $261.00  
  Purchase #6 $210.53   13.641%   $239.2484   $239.25   $239.25   $239.20  
  Purchase #7 $136.97   4.777%   $143.5131   $143.51   $143.50   $143.50  
  7 purchase totals = $1,157.26       $1,268.1454   $1,268.14   $1,268.15   $1,268.10