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 $239.41   9.269%   $261.6009   $261.60   $261.60   $261.60  
  Purchase #2 $235.49   7.576%   $253.3307   $253.33   $253.35   $253.30  
  Purchase #3 $225.62   7.291%   $242.07   $242.07   $242.05   $242.10  
  Purchase #4 $178.60   4.652%   $186.9085   $186.91   $186.90   $186.90  
  Purchase #5 $104.78   3.358%   $108.2985   $108.30   $108.30   $108.30  
  Purchase #6 $194.54   8.523%   $211.1206   $211.12   $211.10   $211.10  
  Purchase #7 $164.96   8.166%   $178.4306   $178.43   $178.45   $178.40  
  7 purchase totals = $1,343.40       $1,441.7598   $1,441.76   $1,441.75   $1,441.70