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	$143.60	11.379%	$159.9402	$159.94	$159.95	$159.90
Purchase #2	$66.87	8.581%	$72.6081	$72.61	$72.60	$72.60
Purchase #3	$127.29	9.400%	$139.2553	$139.26	$139.25	$139.30
Purchase #4	$30.60	9.261%	$33.4339	$33.43	$33.45	$33.40
Purchase #5	$17.91	12.597%	$20.1661	$20.17	$20.15	$20.20
Purchase #6	$229.84	6.313%	$244.3498	$244.35	$244.35	$244.30
Purchase #7	$178.83	5.865%	$189.3184	$189.32	$189.30	$189.30
7 purchase totals =	$794.94		$859.0718	$859.08	$859.05	$859.00