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	$30.56	12.219%	$34.2941	$34.29	$34.30	$34.30
Purchase #2	$123.43	3.819%	$128.1438	$128.14	$128.15	$128.10
Purchase #3	$227.86	11.222%	$253.4304	$253.43	$253.45	$253.40
Purchase #4	$20.44	5.873%	$21.6404	$21.64	$21.65	$21.60
Purchase #5	$211.65	7.333%	$227.1703	$227.17	$227.15	$227.20
Purchase #6	$138.67	4.176%	$144.4609	$144.46	$144.45	$144.50
Purchase #7	$155.52	8.307%	$168.439	$168.44	$168.45	$168.40
7 purchase totals =	$908.13		$977.5789	$977.57	$977.60	$977.50