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 $174.76   10.138%   $192.4772   $192.48   $192.50   $192.50  
  Purchase #2 $173.36   5.634%   $183.1271   $183.13   $183.15   $183.10  
  Purchase #3 $129.38   11.675%   $144.4851   $144.49   $144.50   $144.50  
  Purchase #4 $30.69   12.624%   $34.5643   $34.56   $34.55   $34.60  
  Purchase #5 $236.78   10.720%   $262.1628   $262.16   $262.15   $262.20  
  Purchase #6 $185.76   11.236%   $206.632   $206.63   $206.65   $206.60  
  Purchase #7 $233.67   6.251%   $248.2767   $248.28   $248.30   $248.30  
  7 purchase totals = $1,164.40       $1,271.7252   $1,271.73   $1,271.80   $1,271.80