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	$14.89	12.278%	$16.7182	$16.72	$16.70	$16.70
Purchase #2	$35.65	7.429%	$38.2984	$38.30	$38.30	$38.30
Purchase #3	$50.26	3.354%	$51.9457	$51.95	$51.95	$51.90
Purchase #4	$36.89	4.467%	$38.5379	$38.54	$38.55	$38.50
Purchase #5	$100.64	4.748%	$105.4184	$105.42	$105.40	$105.40
Purchase #6	$115.30	10.482%	$127.3857	$127.39	$127.40	$127.40
Purchase #7	$23.62	9.228%	$25.7997	$25.80	$25.80	$25.80
7 purchase totals =	$377.25		$404.1040	$404.12	$404.10	$404.00