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	$230.34	11.802%	$257.5247	$257.52	$257.50	$257.50
Purchase #2	$121.60	9.236%	$132.831	$132.83	$132.85	$132.80
Purchase #3	$86.47	3.672%	$89.6452	$89.65	$89.65	$89.60
Purchase #4	$50.43	10.483%	$55.7166	$55.72	$55.70	$55.70
Purchase #5	$101.75	9.380%	$111.2942	$111.29	$111.30	$111.30
Purchase #6	$87.36	5.806%	$92.4321	$92.43	$92.45	$92.40
Purchase #7	$45.68	11.216%	$50.8035	$50.80	$50.80	$50.80
7 purchase totals =	$723.63		$790.2473	$790.24	$790.25	$790.10