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 $197.93   11.289%   $220.2743   $220.27   $220.25   $220.30  
  Purchase #2 $65.28   6.466%   $69.501   $69.50   $69.50   $69.50  
  Purchase #3 $103.48   4.261%   $107.8893   $107.89   $107.90   $107.90  
  Purchase #4 $47.35   12.271%   $53.1603   $53.16   $53.15   $53.20  
  Purchase #5 $215.86   8.435%   $234.0678   $234.07   $234.05   $234.10  
  Purchase #6 $167.37   10.795%   $185.4376   $185.44   $185.45   $185.40  
  Purchase #7 $49.77   11.681%   $55.5836   $55.58   $55.60   $55.60  
  7 purchase totals = $847.04       $925.9139   $925.91   $925.90   $926.00