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	$111.65	5.558%	$117.8555	$117.86	$117.85	$117.90
Purchase #2	$120.27	9.252%	$131.3974	$131.40	$131.40	$131.40
Purchase #3	$103.44	12.139%	$115.9966	$116.00	$116.00	$116.00
Purchase #4	$32.80	9.865%	$36.0357	$36.04	$36.05	$36.00
Purchase #5	$15.87	13.183%	$17.9621	$17.96	$17.95	$18.00
Purchase #6	$173.45	13.272%	$196.4703	$196.47	$196.45	$196.50
Purchase #7	$62.76	4.194%	$65.3922	$65.39	$65.40	$65.40
7 purchase totals =	$620.24		$681.1098	$681.12	$681.10	$681.20