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	$129.72	11.142%	$144.1734	$144.17	$144.15	$144.20
Purchase #2	$119.87	13.584%	$136.1531	$136.15	$136.15	$136.20
Purchase #3	$238.38	11.604%	$266.0416	$266.04	$266.05	$266.00
Purchase #4	$126.43	6.276%	$134.3647	$134.36	$134.35	$134.40
Purchase #5	$62.70	6.347%	$66.6796	$66.68	$66.70	$66.70
Purchase #6	$41.51	10.232%	$45.7573	$45.76	$45.75	$45.80
Purchase #7	$24.42	12.342%	$27.4339	$27.43	$27.45	$27.40
7 purchase totals =	$743.03		$820.6036	$820.59	$820.60	$820.70