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 $240.45   12.242%   $269.8859   $269.89   $269.90   $269.90  
  Purchase #2 $178.85   13.265%   $202.5745   $202.57   $202.55   $202.60  
  Purchase #3 $116.59   12.335%   $130.9714   $130.97   $130.95   $131.00  
  Purchase #4 $158.41   13.746%   $180.185   $180.19   $180.20   $180.20  
  Purchase #5 $181.59   6.420%   $193.2481   $193.25   $193.25   $193.20  
  Purchase #6 $195.36   12.181%   $219.1568   $219.16   $219.15   $219.20  
  Purchase #7 $9.89   6.256%   $10.5087   $10.51   $10.50   $10.50  
  7 purchase totals = $1,081.14       $1,206.5304   $1,206.54   $1,206.50   $1,206.60