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	$172.65	9.606%	$189.2348	$189.23	$189.25	$189.20
Purchase #2	$243.30	8.350%	$263.6156	$263.62	$263.60	$263.60
Purchase #3	$164.86	12.113%	$184.8295	$184.83	$184.85	$184.80
Purchase #4	$39.37	10.604%	$43.5448	$43.54	$43.55	$43.50
Purchase #5	$40.84	11.198%	$45.4133	$45.41	$45.40	$45.40
Purchase #6	$61.57	12.170%	$69.0631	$69.06	$69.05	$69.10
Purchase #7	$238.64	7.313%	$256.0917	$256.09	$256.10	$256.10
7 purchase totals =	$961.23		$1,051.7928	$1,051.78	$1,051.80	$1,051.70