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	$209.32	10.560%	$231.4242	$231.42	$231.40	$231.40
Purchase #2	$35.86	9.371%	$39.2204	$39.22	$39.20	$39.20
Purchase #3	$25.68	5.458%	$27.0816	$27.08	$27.10	$27.10
Purchase #4	$52.74	3.837%	$54.7636	$54.76	$54.75	$54.80
Purchase #5	$132.82	7.634%	$142.9595	$142.96	$142.95	$143.00
Purchase #6	$187.47	3.812%	$194.6164	$194.62	$194.60	$194.60
Purchase #7	$127.58	13.298%	$144.5456	$144.55	$144.55	$144.50
7 purchase totals =	$771.47		$834.6113	$834.61	$834.55	$834.60