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	$55.75	6.429%	$59.3342	$59.33	$59.35	$59.30
Purchase #2	$223.87	3.371%	$231.4167	$231.42	$231.40	$231.40
Purchase #3	$99.46	3.126%	$102.5691	$102.57	$102.55	$102.60
Purchase #4	$16.63	13.501%	$18.8752	$18.88	$18.90	$18.90
Purchase #5	$138.68	13.227%	$157.0232	$157.02	$157.00	$157.00
Purchase #6	$89.26	9.441%	$97.687	$97.69	$97.70	$97.70
Purchase #7	$231.85	11.540%	$258.6055	$258.61	$258.60	$258.60
7 purchase totals =	$855.50		$925.5109	$925.52	$925.50	$925.50