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 $233.51   10.781%   $258.6847   $258.68   $258.70   $258.70  
  Purchase #2 $169.30   9.129%   $184.7554   $184.76   $184.75   $184.80  
  Purchase #3 $5.37   4.252%   $5.5983   $5.60   $5.60   $5.60  
  Purchase #4 $167.41   13.801%   $190.5143   $190.51   $190.50   $190.50  
  Purchase #5 $171.94   3.788%   $178.4531   $178.45   $178.45   $178.50  
  Purchase #6 $108.81   5.211%   $114.4801   $114.48   $114.50   $114.50  
  Purchase #7 $172.77   6.505%   $184.0087   $184.01   $184.00   $184.00  
  7 purchase totals = $1,029.11       $1,116.4946   $1,116.49   $1,116.50   $1,116.60