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	$31.42	13.113%	$35.5401	$35.54	$35.55	$35.50
Purchase #2	$65.95	4.267%	$68.7641	$68.76	$68.75	$68.80
Purchase #3	$215.86	10.738%	$239.039	$239.04	$239.05	$239.00
Purchase #4	$77.66	6.663%	$82.8345	$82.83	$82.85	$82.80
Purchase #5	$85.32	5.456%	$89.9751	$89.98	$90.00	$90.00
Purchase #6	$151.95	5.597%	$160.4546	$160.45	$160.45	$160.50
Purchase #7	$115.40	9.140%	$125.9476	$125.95	$125.95	$125.90
7 purchase totals =	$743.56		$802.5550	$802.55	$802.60	$802.50