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	$185.90	10.292%	$205.0328	$205.03	$205.05	$205.00
Purchase #2	$242.40	12.678%	$273.1315	$273.13	$273.15	$273.10
Purchase #3	$206.32	11.276%	$229.5846	$229.58	$229.60	$229.60
Purchase #4	$99.38	3.778%	$103.1346	$103.13	$103.15	$103.10
Purchase #5	$138.80	5.151%	$145.9496	$145.95	$145.95	$145.90
Purchase #6	$156.77	9.746%	$172.0488	$172.05	$172.05	$172.00
Purchase #7	$9.95	5.683%	$10.5155	$10.52	$10.50	$10.50
7 purchase totals =	$1,039.52		$1,139.3974	$1,139.39	$1,139.45	$1,139.20