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	$105.43	10.471%	$116.4696	$116.47	$116.45	$116.50
Purchase #2	$156.30	7.547%	$168.096	$168.10	$168.10	$168.10
Purchase #3	$85.66	4.644%	$89.6381	$89.64	$89.65	$89.60
Purchase #4	$35.75	12.255%	$40.1312	$40.13	$40.15	$40.10
Purchase #5	$94.77	12.628%	$106.7376	$106.74	$106.75	$106.70
Purchase #6	$222.65	4.738%	$233.1992	$233.20	$233.20	$233.20
Purchase #7	$14.29	10.356%	$15.7699	$15.77	$15.75	$15.80
7 purchase totals =	$714.85		$770.0416	$770.05	$770.05	$770.00