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	$21.75	12.344%	$24.4348	$24.43	$24.45	$24.40
Purchase #2	$18.86	9.675%	$20.6847	$20.68	$20.70	$20.70
Purchase #3	$103.65	10.275%	$114.3	$114.30	$114.30	$114.30
Purchase #4	$76.35	12.554%	$85.935	$85.94	$85.95	$85.90
Purchase #5	$47.36	9.805%	$52.0036	$52.00	$52.00	$52.00
Purchase #6	$90.52	11.488%	$100.9189	$100.92	$100.90	$100.90
Purchase #7	$6.86	6.168%	$7.2831	$7.28	$7.30	$7.30
7 purchase totals =	$365.35		$405.5601	$405.55	$405.60	$405.50