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	$136.83	13.661%	$155.5223	$155.52	$155.50	$155.50
Purchase #2	$152.28	4.125%	$158.5616	$158.56	$158.55	$158.60
Purchase #3	$20.96	13.134%	$23.7129	$23.71	$23.70	$23.70
Purchase #4	$74.86	10.431%	$82.6686	$82.67	$82.65	$82.70
Purchase #5	$107.34	4.136%	$111.7796	$111.78	$111.80	$111.80
Purchase #6	$233.67	7.510%	$251.2186	$251.22	$251.20	$251.20
Purchase #7	$118.31	8.458%	$128.3167	$128.32	$128.30	$128.30
7 purchase totals =	$844.25		$911.7803	$911.78	$911.70	$911.80