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 $20.71   5.649%   $21.8799   $21.88   $21.90   $21.90  
  Purchase #2 $129.45   8.850%   $140.9063   $140.91   $140.90   $140.90  
  Purchase #3 $212.87   11.456%   $237.2564   $237.26   $237.25   $237.30  
  Purchase #4 $182.71   6.792%   $195.1197   $195.12   $195.10   $195.10  
  Purchase #5 $83.32   6.262%   $88.5375   $88.54   $88.55   $88.50  
  Purchase #6 $9.99   11.116%   $11.1005   $11.10   $11.10   $11.10  
  Purchase #7 $208.42   6.315%   $221.5817   $221.58   $221.60   $221.60  
  7 purchase totals = $847.47       $916.3820   $916.39   $916.40   $916.40