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	$231.55	4.208%	$241.2936	$241.29	$241.30	$241.30
Purchase #2	$191.51	10.311%	$211.2566	$211.26	$211.25	$211.30
Purchase #3	$43.82	3.826%	$45.4966	$45.50	$45.50	$45.50
Purchase #4	$73.40	12.667%	$82.6976	$82.70	$82.70	$82.70
Purchase #5	$88.43	11.395%	$98.5066	$98.51	$98.50	$98.50
Purchase #6	$31.84	7.196%	$34.1312	$34.13	$34.15	$34.10
Purchase #7	$185.54	6.401%	$197.4164	$197.42	$197.40	$197.40
7 purchase totals =	$846.09		$910.7986	$910.81	$910.80	$910.80