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	$15.86	10.481%	$17.5223	$17.52	$17.50	$17.50
Purchase #2	$49.41	3.240%	$51.0109	$51.01	$51.00	$51.00
Purchase #3	$19.61	5.159%	$20.6217	$20.62	$20.60	$20.60
Purchase #4	$240.91	12.533%	$271.1033	$271.10	$271.10	$271.10
Purchase #5	$178.50	12.518%	$200.8446	$200.84	$200.85	$200.80
Purchase #6	$174.76	9.218%	$190.8694	$190.87	$190.85	$190.90
Purchase #7	$13.89	10.732%	$15.3807	$15.38	$15.40	$15.40
7 purchase totals =	$692.94		$767.3529	$767.34	$767.30	$767.30