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	$48.45	3.806%	$50.294	$50.29	$50.30	$50.30
Purchase #2	$35.57	5.860%	$37.6544	$37.65	$37.65	$37.70
Purchase #3	$207.39	10.167%	$228.4753	$228.48	$228.50	$228.50
Purchase #4	$20.71	8.488%	$22.4679	$22.47	$22.45	$22.50
Purchase #5	$35.45	13.384%	$40.1946	$40.19	$40.20	$40.20
Purchase #6	$21.43	5.405%	$22.5883	$22.59	$22.60	$22.60
Purchase #7	$12.61	11.469%	$14.0562	$14.06	$14.05	$14.10
7 purchase totals =	$381.61		$415.7307	$415.73	$415.75	$415.90