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	$132.38	4.657%	$138.5449	$138.54	$138.55	$138.50
Purchase #2	$99.42	12.262%	$111.6109	$111.61	$111.60	$111.60
Purchase #3	$185.85	6.173%	$197.3225	$197.32	$197.30	$197.30
Purchase #4	$224.84	12.297%	$252.4886	$252.49	$252.50	$252.50
Purchase #5	$66.99	8.694%	$72.8141	$72.81	$72.80	$72.80
Purchase #6	$41.76	13.463%	$47.3821	$47.38	$47.40	$47.40
Purchase #7	$244.78	6.590%	$260.911	$260.91	$260.90	$260.90
7 purchase totals =	$996.02		$1,081.0741	$1,081.06	$1,081.05	$1,081.00