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 $236.87   13.486%   $268.8143   $268.81   $268.80   $268.80  
  Purchase #2 $35.68   5.844%   $37.7651   $37.77   $37.75   $37.80  
  Purchase #3 $227.44   10.244%   $250.739   $250.74   $250.75   $250.70  
  Purchase #4 $176.62   9.773%   $193.8811   $193.88   $193.90   $193.90  
  Purchase #5 $109.61   12.491%   $123.3014   $123.30   $123.30   $123.30  
  Purchase #6 $248.45   8.349%   $269.1931   $269.19   $269.20   $269.20  
  Purchase #7 $69.39   9.349%   $75.8773   $75.88   $75.90   $75.90  
  7 purchase totals = $1,104.06       $1,219.5713   $1,219.57   $1,219.60   $1,219.60