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	$144.69	6.428%	$153.9907	$153.99	$154.00	$154.00
Purchase #2	$68.32	13.666%	$77.6566	$77.66	$77.65	$77.70
Purchase #3	$141.90	7.324%	$152.2928	$152.29	$152.30	$152.30
Purchase #4	$23.42	7.690%	$25.221	$25.22	$25.20	$25.20
Purchase #5	$53.54	6.217%	$56.8686	$56.87	$56.85	$56.90
Purchase #6	$116.49	9.792%	$127.8967	$127.90	$127.90	$127.90
Purchase #7	$80.41	12.142%	$90.1734	$90.17	$90.15	$90.20
7 purchase totals =	$628.77		$684.0998	$684.10	$684.05	$684.20