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	$49.64	3.103%	$51.1803	$51.18	$51.20	$51.20
Purchase #2	$102.72	11.846%	$114.8882	$114.89	$114.90	$114.90
Purchase #3	$101.55	9.762%	$111.4633	$111.46	$111.45	$111.50
Purchase #4	$198.95	4.195%	$207.296	$207.30	$207.30	$207.30
Purchase #5	$225.42	7.286%	$241.8441	$241.84	$241.85	$241.80
Purchase #6	$102.71	11.616%	$114.6408	$114.64	$114.65	$114.60
Purchase #7	$39.72	7.131%	$42.5524	$42.55	$42.55	$42.60
7 purchase totals =	$820.71		$883.8651	$883.86	$883.90	$883.90