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	$203.42	10.388%	$224.5513	$224.55	$224.55	$224.60
Purchase #2	$111.52	10.277%	$122.9809	$122.98	$123.00	$123.00
Purchase #3	$62.86	4.737%	$65.8377	$65.84	$65.85	$65.80
Purchase #4	$173.65	6.588%	$185.0901	$185.09	$185.10	$185.10
Purchase #5	$29.85	12.447%	$33.5654	$33.57	$33.55	$33.60
Purchase #6	$208.41	10.852%	$231.0267	$231.03	$231.05	$231.00
Purchase #7	$101.41	9.477%	$111.0206	$111.02	$111.00	$111.00
7 purchase totals =	$891.12		$974.0727	$974.08	$974.10	$974.10