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 $106.68   11.851%   $119.3226   $119.32   $119.30   $119.30  
  Purchase #2 $58.93   10.106%   $64.8855   $64.89   $64.90   $64.90  
  Purchase #3 $109.38   4.495%   $114.2966   $114.30   $114.30   $114.30  
  Purchase #4 $158.59   11.739%   $177.2069   $177.21   $177.20   $177.20  
  Purchase #5 $241.27   12.847%   $272.266   $272.27   $272.25   $272.30  
  Purchase #6 $176.50   4.347%   $184.1725   $184.17   $184.15   $184.20  
  Purchase #7 $224.55   6.515%   $239.1794   $239.18   $239.20   $239.20  
  7 purchase totals = $1,075.90       $1,171.3295   $1,171.34   $1,171.30   $1,171.40