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	$18.49	12.805%	$20.8576	$20.86	$20.85	$20.90
Purchase #2	$95.30	8.176%	$103.0917	$103.09	$103.10	$103.10
Purchase #3	$85.92	3.776%	$89.1643	$89.16	$89.15	$89.20
Purchase #4	$250.74	5.294%	$264.0142	$264.01	$264.00	$264.00
Purchase #5	$6.97	6.252%	$7.4058	$7.41	$7.40	$7.40
Purchase #6	$152.84	9.114%	$166.7698	$166.77	$166.75	$166.80
Purchase #7	$89.70	4.255%	$93.5167	$93.52	$93.50	$93.50
7 purchase totals =	$699.96		$744.8201	$744.82	$744.75	$744.90