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 $245.76   6.242%   $261.1003   $261.10   $261.10   $261.10  
  Purchase #2 $53.68   8.541%   $58.2648   $58.26   $58.25   $58.30  
  Purchase #3 $79.76   8.556%   $86.5843   $86.58   $86.60   $86.60  
  Purchase #4 $91.57   12.794%   $103.2855   $103.29   $103.30   $103.30  
  Purchase #5 $187.60   3.644%   $194.4361   $194.44   $194.45   $194.40  
  Purchase #6 $163.85   4.648%   $171.4657   $171.47   $171.45   $171.50  
  Purchase #7 $107.36   12.603%   $120.8906   $120.89   $120.90   $120.90  
  7 purchase totals = $929.58       $996.0273   $996.03   $996.05   $996.10