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	$35.85	8.113%	$38.7585	$38.76	$38.75	$38.80
Purchase #2	$126.40	12.183%	$141.7993	$141.80	$141.80	$141.80
Purchase #3	$146.51	8.210%	$158.5385	$158.54	$158.55	$158.50
Purchase #4	$214.86	8.570%	$233.2735	$233.27	$233.25	$233.30
Purchase #5	$39.43	9.380%	$43.1285	$43.13	$43.15	$43.10
Purchase #6	$19.51	6.204%	$20.7204	$20.72	$20.70	$20.70
Purchase #7	$17.69	7.147%	$18.9543	$18.95	$18.95	$19.00
7 purchase totals =	$600.25		$655.1730	$655.17	$655.15	$655.20