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	$233.92	6.705%	$249.6043	$249.60	$249.60	$249.60
Purchase #2	$74.26	8.793%	$80.7897	$80.79	$80.80	$80.80
Purchase #3	$19.42	4.338%	$20.2624	$20.26	$20.25	$20.30
Purchase #4	$98.98	6.582%	$105.4949	$105.49	$105.50	$105.50
Purchase #5	$68.76	5.441%	$72.5012	$72.50	$72.50	$72.50
Purchase #6	$28.47	3.287%	$29.4058	$29.41	$29.40	$29.40
Purchase #7	$139.56	11.133%	$155.0972	$155.10	$155.10	$155.10
7 purchase totals =	$663.37		$713.1555	$713.15	$713.15	$713.20