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	$175.84	12.866%	$198.4636	$198.46	$198.45	$198.50
Purchase #2	$144.25	9.213%	$157.5398	$157.54	$157.55	$157.50
Purchase #3	$217.82	7.332%	$233.7906	$233.79	$233.80	$233.80
Purchase #4	$45.66	5.500%	$48.1713	$48.17	$48.15	$48.20
Purchase #5	$115.52	10.659%	$127.8333	$127.83	$127.85	$127.80
Purchase #6	$35.91	11.617%	$40.0817	$40.08	$40.10	$40.10
Purchase #7	$14.52	5.404%	$15.3047	$15.30	$15.30	$15.30
7 purchase totals =	$749.52		$821.1850	$821.17	$821.20	$821.20