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 $114.62   10.592%   $126.7606   $126.76   $126.75   $126.80  
  Purchase #2 $206.63   6.519%   $220.1002   $220.10   $220.10   $220.10  
  Purchase #3 $230.47   8.154%   $249.2625   $249.26   $249.25   $249.30  
  Purchase #4 $81.66   4.600%   $85.4164   $85.42   $85.40   $85.40  
  Purchase #5 $166.49   12.683%   $187.6059   $187.61   $187.60   $187.60  
  Purchase #6 $32.42   4.296%   $33.8128   $33.81   $33.80   $33.80  
  Purchase #7 $116.85   11.788%   $130.6243   $130.62   $130.60   $130.60  
  7 purchase totals = $949.14       $1,033.5827   $1,033.58   $1,033.50   $1,033.60