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	$183.83	5.828%	$194.5436	$194.54	$194.55	$194.50
Purchase #2	$104.33	13.210%	$118.112	$118.11	$118.10	$118.10
Purchase #3	$164.37	5.235%	$172.9748	$172.97	$172.95	$173.00
Purchase #4	$221.68	9.265%	$242.2187	$242.22	$242.20	$242.20
Purchase #5	$87.76	3.431%	$90.771	$90.77	$90.75	$90.80
Purchase #6	$192.54	13.126%	$217.8128	$217.81	$217.80	$217.80
Purchase #7	$126.79	4.199%	$132.1139	$132.11	$132.10	$132.10
7 purchase totals =	$1,081.30		$1,168.5468	$1,168.53	$1,168.45	$1,168.50