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	$161.58	11.544%	$180.2328	$180.23	$180.25	$180.20
Purchase #2	$34.26	11.329%	$38.1413	$38.14	$38.15	$38.10
Purchase #3	$233.29	13.772%	$265.4187	$265.42	$265.40	$265.40
Purchase #4	$164.83	4.182%	$171.7232	$171.72	$171.70	$171.70
Purchase #5	$153.39	12.333%	$172.3076	$172.31	$172.30	$172.30
Purchase #6	$149.32	13.665%	$169.7246	$169.72	$169.70	$169.70
Purchase #7	$72.39	4.603%	$75.7221	$75.72	$75.70	$75.70
7 purchase totals =	$969.06		$1,073.2703	$1,073.26	$1,073.20	$1,073.10