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	$155.75	8.153%	$168.4483	$168.45	$168.45	$168.40
Purchase #2	$152.71	13.752%	$173.7107	$173.71	$173.70	$173.70
Purchase #3	$122.38	4.340%	$127.6913	$127.69	$127.70	$127.70
Purchase #4	$156.57	7.123%	$167.7225	$167.72	$167.70	$167.70
Purchase #5	$100.29	9.543%	$109.8607	$109.86	$109.85	$109.90
Purchase #6	$104.84	12.719%	$118.1746	$118.17	$118.15	$118.20
Purchase #7	$40.70	10.719%	$45.0626	$45.06	$45.05	$45.10
7 purchase totals =	$833.24		$910.6707	$910.66	$910.60	$910.70