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	$78.56	3.843%	$81.5791	$81.58	$81.60	$81.60
Purchase #2	$136.45	13.233%	$154.5064	$154.51	$154.50	$154.50
Purchase #3	$197.32	9.105%	$215.286	$215.29	$215.30	$215.30
Purchase #4	$29.59	11.858%	$33.0988	$33.10	$33.10	$33.10
Purchase #5	$84.91	4.129%	$88.4159	$88.42	$88.40	$88.40
Purchase #6	$91.31	9.655%	$100.126	$100.13	$100.15	$100.10
Purchase #7	$112.65	4.296%	$117.4894	$117.49	$117.50	$117.50
7 purchase totals =	$730.79		$790.5016	$790.52	$790.55	$790.50