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	$74.59	9.290%	$81.5194	$81.52	$81.50	$81.50
Purchase #2	$30.64	3.663%	$31.7623	$31.76	$31.75	$31.80
Purchase #3	$34.26	13.435%	$38.8628	$38.86	$38.85	$38.90
Purchase #4	$48.66	10.269%	$53.6569	$53.66	$53.65	$53.70
Purchase #5	$41.95	10.333%	$46.2847	$46.28	$46.30	$46.30
Purchase #6	$230.82	10.172%	$254.299	$254.30	$254.30	$254.30
Purchase #7	$75.90	3.817%	$78.7971	$78.80	$78.80	$78.80
7 purchase totals =	$536.82		$585.1822	$585.18	$585.15	$585.30