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	$36.78	8.509%	$39.9096	$39.91	$39.90	$39.90
Purchase #2	$240.79	13.376%	$272.9981	$273.00	$273.00	$273.00
Purchase #3	$242.55	3.687%	$251.4928	$251.49	$251.50	$251.50
Purchase #4	$159.35	10.337%	$175.822	$175.82	$175.80	$175.80
Purchase #5	$87.81	3.481%	$90.8667	$90.87	$90.85	$90.90
Purchase #6	$94.91	11.240%	$105.5779	$105.58	$105.60	$105.60
Purchase #7	$173.83	8.114%	$187.9346	$187.93	$187.95	$187.90
7 purchase totals =	$1,036.02		$1,124.6017	$1,124.60	$1,124.60	$1,124.60