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	$24.75	12.478%	$27.8383	$27.84	$27.85	$27.80
Purchase #2	$111.74	13.719%	$127.0696	$127.07	$127.05	$127.10
Purchase #3	$19.67	6.106%	$20.8711	$20.87	$20.85	$20.90
Purchase #4	$48.53	10.285%	$53.5213	$53.52	$53.50	$53.50
Purchase #5	$118.29	3.680%	$122.6431	$122.64	$122.65	$122.60
Purchase #6	$111.82	12.233%	$125.4989	$125.50	$125.50	$125.50
Purchase #7	$109.90	3.211%	$113.4289	$113.43	$113.45	$113.40
7 purchase totals =	$544.70		$590.8712	$590.87	$590.85	$590.80