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	$124.71	6.322%	$132.5942	$132.59	$132.60	$132.60
Purchase #2	$202.30	9.353%	$221.2211	$221.22	$221.20	$221.20
Purchase #3	$128.25	8.847%	$139.5963	$139.60	$139.60	$139.60
Purchase #4	$29.96	10.260%	$33.0339	$33.03	$33.05	$33.00
Purchase #5	$233.70	9.412%	$255.6958	$255.70	$255.70	$255.70
Purchase #6	$103.37	10.868%	$114.6043	$114.60	$114.60	$114.60
Purchase #7	$62.54	4.162%	$65.1429	$65.14	$65.15	$65.10
7 purchase totals =	$884.83		$961.8885	$961.88	$961.90	$961.80