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	$45.40	10.249%	$50.053	$50.05	$50.05	$50.10
Purchase #2	$124.27	12.492%	$139.7938	$139.79	$139.80	$139.80
Purchase #3	$129.63	11.738%	$144.846	$144.85	$144.85	$144.80
Purchase #4	$9.91	9.662%	$10.8675	$10.87	$10.85	$10.90
Purchase #5	$138.60	9.106%	$151.2209	$151.22	$151.20	$151.20
Purchase #6	$188.75	13.623%	$214.4634	$214.46	$214.45	$214.50
Purchase #7	$29.29	12.448%	$32.936	$32.94	$32.95	$32.90
7 purchase totals =	$665.85		$744.1806	$744.18	$744.15	$744.20