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	$104.66	4.717%	$109.5968	$109.60	$109.60	$109.60
Purchase #2	$147.52	12.113%	$165.3891	$165.39	$165.40	$165.40
Purchase #3	$21.41	9.550%	$23.4547	$23.45	$23.45	$23.50
Purchase #4	$51.72	3.102%	$53.3244	$53.32	$53.30	$53.30
Purchase #5	$46.98	5.836%	$49.7218	$49.72	$49.70	$49.70
Purchase #6	$150.97	13.675%	$171.6151	$171.62	$171.60	$171.60
Purchase #7	$231.45	10.185%	$255.0232	$255.02	$255.00	$255.00
7 purchase totals =	$754.71		$828.1251	$828.12	$828.05	$828.10