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 $32.58   5.162%   $34.2618   $34.26   $34.25   $34.30  
  Purchase #2 $153.58   5.632%   $162.2296   $162.23   $162.25   $162.20  
  Purchase #3 $123.83   7.676%   $133.3352   $133.34   $133.35   $133.30  
  Purchase #4 $186.95   4.421%   $195.2151   $195.22   $195.20   $195.20  
  Purchase #5 $44.43   8.405%   $48.1643   $48.16   $48.15   $48.20  
  Purchase #6 $81.45   3.585%   $84.37   $84.37   $84.35   $84.40  
  Purchase #7 $239.52   9.249%   $261.6732   $261.67   $261.65   $261.70  
  7 purchase totals = $862.34       $919.2492   $919.25   $919.20   $919.30