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	$179.85	11.247%	$200.0777	$200.08	$200.10	$200.10
Purchase #2	$47.76	5.383%	$50.3309	$50.33	$50.35	$50.30
Purchase #3	$85.63	12.634%	$96.4485	$96.45	$96.45	$96.40
Purchase #4	$111.43	5.156%	$117.1753	$117.18	$117.20	$117.20
Purchase #5	$91.32	13.727%	$103.8555	$103.86	$103.85	$103.90
Purchase #6	$189.28	9.518%	$207.2957	$207.30	$207.30	$207.30
Purchase #7	$111.40	4.586%	$116.5088	$116.51	$116.50	$116.50
7 purchase totals =	$816.67		$891.6924	$891.71	$891.75	$891.70