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	$207.36	10.197%	$228.5045	$228.50	$228.50	$228.50
Purchase #2	$11.98	4.457%	$12.5139	$12.51	$12.50	$12.50
Purchase #3	$87.92	12.329%	$98.7597	$98.76	$98.75	$98.80
Purchase #4	$49.91	9.194%	$54.4987	$54.50	$54.50	$54.50
Purchase #5	$83.26	8.752%	$90.5469	$90.55	$90.55	$90.50
Purchase #6	$101.59	6.615%	$108.3102	$108.31	$108.30	$108.30
Purchase #7	$84.64	7.684%	$91.1437	$91.14	$91.15	$91.10
7 purchase totals =	$626.66		$684.2776	$684.27	$684.25	$684.20