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	$230.64	8.640%	$250.5673	$250.57	$250.55	$250.60
Purchase #2	$84.32	6.722%	$89.988	$89.99	$90.00	$90.00
Purchase #3	$166.87	4.509%	$174.3942	$174.39	$174.40	$174.40
Purchase #4	$226.42	12.759%	$255.3089	$255.31	$255.30	$255.30
Purchase #5	$41.66	3.408%	$43.0798	$43.08	$43.10	$43.10
Purchase #6	$186.27	6.765%	$198.8712	$198.87	$198.85	$198.90
Purchase #7	$66.77	13.218%	$75.5957	$75.60	$75.60	$75.60
7 purchase totals =	$1,002.95		$1,087.8051	$1,087.81	$1,087.80	$1,087.90