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 $200.43   6.747%   $213.953   $213.95   $213.95   $214.00  
  Purchase #2 $76.97   6.375%   $81.8768   $81.88   $81.90   $81.90  
  Purchase #3 $226.77   9.583%   $248.5014   $248.50   $248.50   $248.50  
  Purchase #4 $168.71   8.534%   $183.1077   $183.11   $183.10   $183.10  
  Purchase #5 $37.77   7.524%   $40.6118   $40.61   $40.60   $40.60  
  Purchase #6 $11.25   5.485%   $11.8671   $11.87   $11.85   $11.90  
  Purchase #7 $22.28   11.861%   $24.9226   $24.92   $24.90   $24.90  
  7 purchase totals = $744.18       $804.8404   $804.84   $804.80   $804.90