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	$90.63	13.650%	$103.001	$103.00	$103.00	$103.00
Purchase #2	$127.29	13.182%	$144.0694	$144.07	$144.05	$144.10
Purchase #3	$29.37	9.427%	$32.1387	$32.14	$32.15	$32.10
Purchase #4	$162.86	10.139%	$179.3724	$179.37	$179.35	$179.40
Purchase #5	$26.93	10.351%	$29.7175	$29.72	$29.70	$29.70
Purchase #6	$71.84	4.163%	$74.8307	$74.83	$74.85	$74.80
Purchase #7	$171.98	4.440%	$179.6159	$179.62	$179.60	$179.60
7 purchase totals =	$680.90		$742.7456	$742.75	$742.70	$742.70