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	$47.59	3.278%	$49.15	$49.15	$49.15	$49.20
Purchase #2	$89.65	3.129%	$92.4551	$92.46	$92.45	$92.50
Purchase #3	$49.68	9.550%	$54.4244	$54.42	$54.40	$54.40
Purchase #4	$150.28	10.335%	$165.8114	$165.81	$165.80	$165.80
Purchase #5	$8.27	6.247%	$8.7866	$8.79	$8.80	$8.80
Purchase #6	$103.44	13.285%	$117.182	$117.18	$117.20	$117.20
Purchase #7	$80.47	11.236%	$89.5116	$89.51	$89.50	$89.50
7 purchase totals =	$529.38		$577.3211	$577.32	$577.30	$577.40