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 $101.52   12.326%   $114.0334   $114.03   $114.05   $114.00  
  Purchase #2 $248.36   13.494%   $281.8737   $281.87   $281.85   $281.90  
  Purchase #3 $21.65   7.389%   $23.2497   $23.25   $23.25   $23.20  
  Purchase #4 $86.26   6.269%   $91.6676   $91.67   $91.65   $91.70  
  Purchase #5 $72.99   4.600%   $76.3475   $76.35   $76.35   $76.30  
  Purchase #6 $226.86   4.724%   $237.5769   $237.58   $237.60   $237.60  
  Purchase #7 $150.57   3.574%   $155.9514   $155.95   $155.95   $156.00  
  7 purchase totals = $908.21       $980.7002   $980.70   $980.70   $980.70