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	$72.27	9.182%	$78.9058	$78.91	$78.90	$78.90
Purchase #2	$223.84	13.647%	$254.3874	$254.39	$254.40	$254.40
Purchase #3	$204.26	5.561%	$215.6189	$215.62	$215.60	$215.60
Purchase #4	$143.90	7.249%	$154.3313	$154.33	$154.35	$154.30
Purchase #5	$127.48	7.522%	$137.069	$137.07	$137.05	$137.10
Purchase #6	$117.41	8.103%	$126.9237	$126.92	$126.90	$126.90
Purchase #7	$244.43	4.692%	$255.8987	$255.90	$255.90	$255.90
7 purchase totals =	$1,133.59		$1,223.1348	$1,223.14	$1,223.10	$1,223.10