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	$139.52	13.633%	$158.5408	$158.54	$158.55	$158.50
Purchase #2	$111.40	8.152%	$120.4813	$120.48	$120.50	$120.50
Purchase #3	$170.86	4.734%	$178.9485	$178.95	$178.95	$178.90
Purchase #4	$143.36	11.561%	$159.9338	$159.93	$159.95	$159.90
Purchase #5	$105.78	5.608%	$111.7121	$111.71	$111.70	$111.70
Purchase #6	$233.84	12.388%	$262.8081	$262.81	$262.80	$262.80
Purchase #7	$23.61	13.841%	$26.8779	$26.88	$26.90	$26.90
7 purchase totals =	$928.37		$1,019.3025	$1,019.30	$1,019.35	$1,019.20