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	$37.64	11.687%	$42.039	$42.04	$42.05	$42.00
Purchase #2	$241.94	5.113%	$254.3104	$254.31	$254.30	$254.30
Purchase #3	$50.29	5.390%	$53.0006	$53.00	$53.00	$53.00
Purchase #4	$177.55	12.339%	$199.4579	$199.46	$199.45	$199.50
Purchase #5	$134.31	12.258%	$150.7737	$150.77	$150.75	$150.80
Purchase #6	$122.78	3.808%	$127.4555	$127.46	$127.45	$127.50
Purchase #7	$13.79	4.584%	$14.4221	$14.42	$14.40	$14.40
7 purchase totals =	$778.30		$841.4592	$841.46	$841.40	$841.50