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	$65.87	4.856%	$69.0686	$69.07	$69.05	$69.10
Purchase #2	$39.96	4.569%	$41.7858	$41.79	$41.80	$41.80
Purchase #3	$89.84	10.330%	$99.1205	$99.12	$99.10	$99.10
Purchase #4	$244.36	9.465%	$267.4887	$267.49	$267.50	$267.50
Purchase #5	$115.41	10.783%	$127.8547	$127.85	$127.85	$127.90
Purchase #6	$22.36	5.303%	$23.5458	$23.55	$23.55	$23.50
Purchase #7	$9.30	10.396%	$10.2668	$10.27	$10.25	$10.30
7 purchase totals =	$587.10		$639.1309	$639.14	$639.10	$639.20