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	$134.51	6.842%	$143.7132	$143.71	$143.70	$143.70
Purchase #2	$81.41	9.531%	$89.1692	$89.17	$89.15	$89.20
Purchase #3	$46.80	11.313%	$52.0945	$52.09	$52.10	$52.10
Purchase #4	$244.86	4.772%	$256.5447	$256.54	$256.55	$256.50
Purchase #5	$78.71	10.207%	$86.7439	$86.74	$86.75	$86.70
Purchase #6	$211.86	10.122%	$233.3045	$233.30	$233.30	$233.30
Purchase #7	$27.52	7.567%	$29.6024	$29.60	$29.60	$29.60
7 purchase totals =	$825.67		$891.1724	$891.15	$891.15	$891.10