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	$242.58	5.847%	$256.7637	$256.76	$256.75	$256.80
Purchase #2	$132.52	8.276%	$143.4874	$143.49	$143.50	$143.50
Purchase #3	$67.31	3.627%	$69.7513	$69.75	$69.75	$69.80
Purchase #4	$80.36	11.258%	$89.4069	$89.41	$89.40	$89.40
Purchase #5	$27.64	10.823%	$30.6315	$30.63	$30.65	$30.60
Purchase #6	$100.82	4.594%	$105.4517	$105.45	$105.45	$105.50
Purchase #7	$90.87	10.637%	$100.5358	$100.54	$100.55	$100.50
7 purchase totals =	$742.10		$796.0283	$796.03	$796.05	$796.10