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 $54.77   4.773%   $57.3842   $57.38   $57.40   $57.40  
  Purchase #2 $222.33   8.874%   $242.0596   $242.06   $242.05   $242.10  
  Purchase #3 $79.98   8.667%   $86.9119   $86.91   $86.90   $86.90  
  Purchase #4 $227.40   11.528%   $253.6147   $253.61   $253.60   $253.60  
  Purchase #5 $10.76   11.290%   $11.9748   $11.97   $11.95   $12.00  
  Purchase #6 $183.35   7.569%   $197.2278   $197.23   $197.25   $197.20  
  Purchase #7 $248.99   6.240%   $264.527   $264.53   $264.55   $264.50  
  7 purchase totals = $1,027.58       $1,113.7000   $1,113.69   $1,113.70   $1,113.70