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	$18.45	5.641%	$19.4908	$19.49	$19.50	$19.50
Purchase #2	$215.80	3.695%	$223.7738	$223.77	$223.75	$223.80
Purchase #3	$122.71	3.863%	$127.4503	$127.45	$127.45	$127.50
Purchase #4	$134.42	13.255%	$152.2374	$152.24	$152.25	$152.20
Purchase #5	$171.37	4.830%	$179.6472	$179.65	$179.65	$179.60
Purchase #6	$125.86	3.371%	$130.1027	$130.10	$130.10	$130.10
Purchase #7	$10.30	3.131%	$10.6225	$10.62	$10.60	$10.60
7 purchase totals =	$798.91		$843.3247	$843.32	$843.30	$843.30