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	$124.41	12.657%	$140.1566	$140.16	$140.15	$140.20
Purchase #2	$183.91	8.788%	$200.072	$200.07	$200.05	$200.10
Purchase #3	$95.32	9.404%	$104.2839	$104.28	$104.30	$104.30
Purchase #4	$143.65	7.773%	$154.8159	$154.82	$154.80	$154.80
Purchase #5	$65.87	10.359%	$72.6935	$72.69	$72.70	$72.70
Purchase #6	$65.79	5.626%	$69.4913	$69.49	$69.50	$69.50
Purchase #7	$89.60	12.396%	$100.7068	$100.71	$100.70	$100.70
7 purchase totals =	$768.55		$842.2200	$842.22	$842.20	$842.30