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	$153.25	8.340%	$166.0311	$166.03	$166.05	$166.00
Purchase #2	$81.28	6.517%	$86.577	$86.58	$86.60	$86.60
Purchase #3	$15.64	12.802%	$17.6422	$17.64	$17.65	$17.60
Purchase #4	$82.76	8.259%	$89.5951	$89.60	$89.60	$89.60
Purchase #5	$30.54	5.323%	$32.1656	$32.17	$32.15	$32.20
Purchase #6	$46.67	3.536%	$48.3203	$48.32	$48.30	$48.30
Purchase #7	$211.46	5.261%	$222.5849	$222.58	$222.60	$222.60
7 purchase totals =	$621.60		$662.9162	$662.92	$662.95	$662.90