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 $247.25   5.838%   $261.6845   $261.68   $261.70   $261.70  
  Purchase #2 $63.28   4.699%   $66.2535   $66.25   $66.25   $66.30  
  Purchase #3 $183.48   13.789%   $208.7801   $208.78   $208.80   $208.80  
  Purchase #4 $222.67   9.821%   $244.5384   $244.54   $244.55   $244.50  
  Purchase #5 $22.50   7.247%   $24.1306   $24.13   $24.15   $24.10  
  Purchase #6 $26.32   12.442%   $29.5947   $29.59   $29.60   $29.60  
  Purchase #7 $239.35   10.798%   $265.195   $265.20   $265.20   $265.20  
  7 purchase totals = $1,004.85       $1,100.1768   $1,100.17   $1,100.25   $1,100.20