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	$231.83	6.659%	$247.2676	$247.27	$247.25	$247.30
Purchase #2	$196.97	9.212%	$215.1149	$215.11	$215.10	$215.10
Purchase #3	$136.41	8.106%	$147.4674	$147.47	$147.45	$147.50
Purchase #4	$153.65	9.716%	$168.5786	$168.58	$168.60	$168.60
Purchase #5	$177.94	10.316%	$196.2963	$196.30	$196.30	$196.30
Purchase #6	$23.28	6.141%	$24.7096	$24.71	$24.70	$24.70
Purchase #7	$208.68	6.747%	$222.7596	$222.76	$222.75	$222.80
7 purchase totals =	$1,128.76		$1,222.1940	$1,222.20	$1,222.15	$1,222.30