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	$68.31	6.136%	$72.5015	$72.50	$72.50	$72.50
Purchase #2	$79.28	11.685%	$88.5439	$88.54	$88.55	$88.50
Purchase #3	$65.42	10.602%	$72.3558	$72.36	$72.35	$72.40
Purchase #4	$184.75	7.519%	$198.6414	$198.64	$198.65	$198.60
Purchase #5	$145.79	8.366%	$157.9868	$157.99	$158.00	$158.00
Purchase #6	$43.97	13.305%	$49.8202	$49.82	$49.80	$49.80
Purchase #7	$84.73	6.751%	$90.4501	$90.45	$90.45	$90.50
7 purchase totals =	$672.25		$730.2997	$730.30	$730.30	$730.30