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 $114.51   13.699%   $130.1967   $130.20   $130.20   $130.20  
  Purchase #2 $141.68   4.394%   $147.9054   $147.91   $147.90   $147.90  
  Purchase #3 $213.27   6.243%   $226.5844   $226.58   $226.60   $226.60  
  Purchase #4 $164.74   7.737%   $177.4859   $177.49   $177.50   $177.50  
  Purchase #5 $116.68   4.798%   $122.2783   $122.28   $122.30   $122.30  
  Purchase #6 $240.69   3.288%   $248.6039   $248.60   $248.60   $248.60  
  Purchase #7 $22.84   7.164%   $24.4763   $24.48   $24.50   $24.50  
  7 purchase totals = $1,014.41       $1,077.5309   $1,077.54   $1,077.60   $1,077.60