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	$65.40	7.855%	$70.5372	$70.54	$70.55	$70.50
Purchase #2	$80.62	5.450%	$85.0138	$85.01	$85.00	$85.00
Purchase #3	$118.82	9.722%	$130.3717	$130.37	$130.35	$130.40
Purchase #4	$41.52	10.580%	$45.9128	$45.91	$45.90	$45.90
Purchase #5	$13.37	3.410%	$13.8259	$13.83	$13.85	$13.80
Purchase #6	$212.69	5.464%	$224.3114	$224.31	$224.30	$224.30
Purchase #7	$106.82	7.429%	$114.7557	$114.76	$114.75	$114.80
7 purchase totals =	$639.24		$684.7285	$684.73	$684.70	$684.70