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	$37.33	12.599%	$42.0332	$42.03	$42.05	$42.00
Purchase #2	$75.80	6.326%	$80.5951	$80.60	$80.60	$80.60
Purchase #3	$37.99	5.313%	$40.0084	$40.01	$40.00	$40.00
Purchase #4	$157.78	9.494%	$172.7596	$172.76	$172.75	$172.80
Purchase #5	$120.26	11.652%	$134.2727	$134.27	$134.25	$134.30
Purchase #6	$118.93	7.486%	$127.8331	$127.83	$127.85	$127.80
Purchase #7	$24.81	6.281%	$26.3683	$26.37	$26.35	$26.40
7 purchase totals =	$572.90		$623.8704	$623.87	$623.85	$623.90