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	$129.54	8.241%	$140.2154	$140.22	$140.20	$140.20
Purchase #2	$243.47	4.674%	$254.8498	$254.85	$254.85	$254.80
Purchase #3	$29.37	13.320%	$33.2821	$33.28	$33.30	$33.30
Purchase #4	$124.45	10.584%	$137.6218	$137.62	$137.60	$137.60
Purchase #5	$155.72	11.142%	$173.0703	$173.07	$173.05	$173.10
Purchase #6	$75.46	9.622%	$82.7208	$82.72	$82.70	$82.70
Purchase #7	$78.70	9.191%	$85.9333	$85.93	$85.95	$85.90
7 purchase totals =	$836.71		$907.6935	$907.69	$907.65	$907.60