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	$82.64	8.724%	$89.8495	$89.85	$89.85	$89.80
Purchase #2	$17.82	11.205%	$19.8167	$19.82	$19.80	$19.80
Purchase #3	$81.42	10.837%	$90.2435	$90.24	$90.25	$90.20
Purchase #4	$133.73	3.247%	$138.0722	$138.07	$138.05	$138.10
Purchase #5	$20.60	9.581%	$22.5737	$22.57	$22.55	$22.60
Purchase #6	$161.65	3.525%	$167.3482	$167.35	$167.35	$167.30
Purchase #7	$105.53	4.728%	$110.5195	$110.52	$110.50	$110.50
7 purchase totals =	$603.39		$638.4233	$638.42	$638.35	$638.30