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	$126.41	13.252%	$143.1619	$143.16	$143.15	$143.20
Purchase #2	$206.90	13.240%	$234.2936	$234.29	$234.30	$234.30
Purchase #3	$33.73	6.250%	$35.8381	$35.84	$35.85	$35.80
Purchase #4	$219.43	10.786%	$243.0977	$243.10	$243.10	$243.10
Purchase #5	$46.83	10.640%	$51.8127	$51.81	$51.80	$51.80
Purchase #6	$58.42	12.420%	$65.6758	$65.68	$65.70	$65.70
Purchase #7	$130.32	5.215%	$137.1162	$137.12	$137.10	$137.10
7 purchase totals =	$822.04		$910.9960	$911.00	$911.00	$911.00