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	$242.69	5.181%	$255.2638	$255.26	$255.25	$255.30
Purchase #2	$48.42	7.516%	$52.0592	$52.06	$52.05	$52.10
Purchase #3	$171.48	4.388%	$179.0045	$179.00	$179.00	$179.00
Purchase #4	$87.77	12.382%	$98.6377	$98.64	$98.65	$98.60
Purchase #5	$10.52	10.366%	$11.6105	$11.61	$11.60	$11.60
Purchase #6	$74.93	9.640%	$82.1533	$82.15	$82.15	$82.20
Purchase #7	$102.46	12.140%	$114.8986	$114.90	$114.90	$114.90
7 purchase totals =	$738.27		$793.6276	$793.62	$793.60	$793.70