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	$226.91	12.184%	$254.5567	$254.56	$254.55	$254.60
Purchase #2	$67.43	6.794%	$72.0112	$72.01	$72.00	$72.00
Purchase #3	$140.98	10.240%	$155.4164	$155.42	$155.40	$155.40
Purchase #4	$187.81	7.598%	$202.0798	$202.08	$202.10	$202.10
Purchase #5	$111.39	6.745%	$118.9033	$118.90	$118.90	$118.90
Purchase #6	$232.75	9.753%	$255.4501	$255.45	$255.45	$255.50
Purchase #7	$172.42	11.440%	$192.1448	$192.14	$192.15	$192.10
7 purchase totals =	$1,139.69		$1,250.5623	$1,250.56	$1,250.55	$1,250.60