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	$38.43	4.226%	$40.0541	$40.05	$40.05	$40.10
Purchase #2	$31.81	4.708%	$33.3076	$33.31	$33.30	$33.30
Purchase #3	$112.91	12.614%	$127.1525	$127.15	$127.15	$127.20
Purchase #4	$114.69	3.276%	$118.4472	$118.45	$118.45	$118.40
Purchase #5	$32.38	4.236%	$33.7516	$33.75	$33.75	$33.80
Purchase #6	$123.51	8.367%	$133.8441	$133.84	$133.85	$133.80
Purchase #7	$89.74	10.608%	$99.2596	$99.26	$99.25	$99.30
7 purchase totals =	$543.47		$585.8167	$585.81	$585.80	$585.90