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	$175.46	7.240%	$188.1633	$188.16	$188.15	$188.20
Purchase #2	$163.72	5.686%	$173.0291	$173.03	$173.05	$173.00
Purchase #3	$36.45	10.518%	$40.2838	$40.28	$40.30	$40.30
Purchase #4	$46.51	12.493%	$52.3205	$52.32	$52.30	$52.30
Purchase #5	$201.86	12.246%	$226.5798	$226.58	$226.60	$226.60
Purchase #6	$244.77	13.677%	$278.2472	$278.25	$278.25	$278.20
Purchase #7	$136.76	3.481%	$141.5206	$141.52	$141.50	$141.50
7 purchase totals =	$1,005.53		$1,100.1443	$1,100.14	$1,100.15	$1,100.10