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	$82.38	8.492%	$89.3757	$89.38	$89.40	$89.40
Purchase #2	$108.86	7.113%	$116.6032	$116.60	$116.60	$116.60
Purchase #3	$178.30	9.813%	$195.7966	$195.80	$195.80	$195.80
Purchase #4	$108.93	9.128%	$118.8731	$118.87	$118.85	$118.90
Purchase #5	$62.25	5.643%	$65.7628	$65.76	$65.75	$65.80
Purchase #6	$212.91	13.852%	$242.4023	$242.40	$242.40	$242.40
Purchase #7	$82.62	3.252%	$85.3068	$85.31	$85.30	$85.30
7 purchase totals =	$836.25		$914.1205	$914.12	$914.10	$914.20