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 $185.77   12.649%   $209.268   $209.27   $209.25   $209.30  
  Purchase #2 $84.28   13.867%   $95.9671   $95.97   $95.95   $96.00  
  Purchase #3 $248.87   11.777%   $278.1794   $278.18   $278.20   $278.20  
  Purchase #4 $237.92   8.263%   $257.5793   $257.58   $257.60   $257.60  
  Purchase #5 $217.53   8.283%   $235.548   $235.55   $235.55   $235.50  
  Purchase #6 $186.68   10.429%   $206.1489   $206.15   $206.15   $206.10  
  Purchase #7 $208.64   5.699%   $220.5304   $220.53   $220.55   $220.50  
  7 purchase totals = $1,369.69       $1,503.2211   $1,503.23   $1,503.25   $1,503.20