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 $207.99   13.718%   $236.5221   $236.52   $236.50   $236.50  
  Purchase #2 $38.43   12.306%   $43.1592   $43.16   $43.15   $43.20  
  Purchase #3 $227.38   9.122%   $248.1216   $248.12   $248.10   $248.10  
  Purchase #4 $170.83   13.288%   $193.5299   $193.53   $193.55   $193.50  
  Purchase #5 $35.25   4.285%   $36.7605   $36.76   $36.75   $36.80  
  Purchase #6 $111.62   5.632%   $117.9064   $117.91   $117.90   $117.90  
  Purchase #7 $230.37   9.720%   $252.762   $252.76   $252.75   $252.80  
  7 purchase totals = $1,021.87       $1,128.7617   $1,128.76   $1,128.70   $1,128.80