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	$24.85	10.738%	$27.5184	$27.52	$27.50	$27.50
Purchase #2	$41.77	5.131%	$43.9132	$43.91	$43.90	$43.90
Purchase #3	$223.84	6.673%	$238.7768	$238.78	$238.80	$238.80
Purchase #4	$233.94	6.137%	$248.2969	$248.30	$248.30	$248.30
Purchase #5	$111.78	10.269%	$123.2587	$123.26	$123.25	$123.30
Purchase #6	$197.49	13.343%	$223.8411	$223.84	$223.85	$223.80
Purchase #7	$9.68	3.874%	$10.055	$10.06	$10.05	$10.10
7 purchase totals =	$843.35		$915.6601	$915.67	$915.65	$915.70