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 $117.84   3.755%   $122.2649   $122.26   $122.25   $122.30  
  Purchase #2 $221.35   12.296%   $248.5672   $248.57   $248.55   $248.60  
  Purchase #3 $207.74   12.388%   $233.4748   $233.47   $233.45   $233.50  
  Purchase #4 $22.65   10.466%   $25.0205   $25.02   $25.00   $25.00  
  Purchase #5 $44.85   13.412%   $50.8653   $50.87   $50.85   $50.90  
  Purchase #6 $246.45   6.212%   $261.7595   $261.76   $261.75   $261.80  
  Purchase #7 $57.50   11.335%   $64.0176   $64.02   $64.00   $64.00  
  7 purchase totals = $918.38       $1,005.9698   $1,005.97   $1,005.85   $1,006.10