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	$104.92	12.747%	$118.2942	$118.29	$118.30	$118.30
Purchase #2	$62.39	5.759%	$65.983	$65.98	$66.00	$66.00
Purchase #3	$33.44	13.425%	$37.9293	$37.93	$37.95	$37.90
Purchase #4	$206.47	13.115%	$233.5485	$233.55	$233.55	$233.50
Purchase #5	$132.61	7.544%	$142.6141	$142.61	$142.60	$142.60
Purchase #6	$50.82	4.618%	$53.1669	$53.17	$53.15	$53.20
Purchase #7	$197.52	8.607%	$214.5205	$214.52	$214.50	$214.50
7 purchase totals =	$788.17		$866.0565	$866.05	$866.05	$866.00