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	$236.82	12.443%	$266.2875	$266.29	$266.30	$266.30
Purchase #2	$38.49	7.315%	$41.3055	$41.31	$41.30	$41.30
Purchase #3	$81.32	10.258%	$89.6618	$89.66	$89.65	$89.70
Purchase #4	$130.78	10.348%	$144.3131	$144.31	$144.30	$144.30
Purchase #5	$202.94	6.422%	$215.9728	$215.97	$215.95	$216.00
Purchase #6	$197.82	8.245%	$214.1303	$214.13	$214.15	$214.10
Purchase #7	$82.25	5.259%	$86.5755	$86.58	$86.60	$86.60
7 purchase totals =	$970.42		$1,058.2465	$1,058.25	$1,058.25	$1,058.30