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	$233.75	12.674%	$263.3755	$263.38	$263.40	$263.40
Purchase #2	$40.37	12.459%	$45.3997	$45.40	$45.40	$45.40
Purchase #3	$132.75	3.248%	$137.0617	$137.06	$137.05	$137.10
Purchase #4	$107.32	3.844%	$111.4454	$111.45	$111.45	$111.40
Purchase #5	$150.96	4.832%	$158.2544	$158.25	$158.25	$158.30
Purchase #6	$142.31	3.201%	$146.8653	$146.87	$146.85	$146.90
Purchase #7	$52.70	5.343%	$55.5158	$55.52	$55.50	$55.50
7 purchase totals =	$860.16		$917.9178	$917.93	$917.90	$918.00