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	$99.49	3.692%	$103.1632	$103.16	$103.15	$103.20
Purchase #2	$82.57	7.497%	$88.7603	$88.76	$88.75	$88.80
Purchase #3	$91.84	8.171%	$99.3442	$99.34	$99.35	$99.30
Purchase #4	$103.72	11.295%	$115.4352	$115.44	$115.45	$115.40
Purchase #5	$90.55	3.782%	$93.9746	$93.97	$93.95	$94.00
Purchase #6	$100.74	10.801%	$111.6209	$111.62	$111.60	$111.60
Purchase #7	$62.29	5.706%	$65.8443	$65.84	$65.85	$65.80
7 purchase totals =	$631.20		$678.1427	$678.13	$678.10	$678.10