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	$85.98	13.826%	$97.8676	$97.87	$97.85	$97.90
Purchase #2	$77.96	11.154%	$86.6557	$86.66	$86.65	$86.70
Purchase #3	$31.98	9.723%	$35.0894	$35.09	$35.10	$35.10
Purchase #4	$118.94	10.272%	$131.1575	$131.16	$131.15	$131.20
Purchase #5	$233.85	4.123%	$243.4916	$243.49	$243.50	$243.50
Purchase #6	$10.26	5.387%	$10.8127	$10.81	$10.80	$10.80
Purchase #7	$35.75	11.819%	$39.9753	$39.98	$40.00	$40.00
7 purchase totals =	$594.72		$645.0498	$645.06	$645.05	$645.20