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	$93.32	10.640%	$103.2492	$103.25	$103.25	$103.20
Purchase #2	$71.33	4.611%	$74.619	$74.62	$74.60	$74.60
Purchase #3	$189.88	8.236%	$205.5185	$205.52	$205.50	$205.50
Purchase #4	$172.96	3.284%	$178.64	$178.64	$178.65	$178.60
Purchase #5	$83.40	8.458%	$90.454	$90.45	$90.45	$90.50
Purchase #6	$151.70	5.346%	$159.8099	$159.81	$159.80	$159.80
Purchase #7	$233.29	4.396%	$243.5454	$243.55	$243.55	$243.50
7 purchase totals =	$995.88		$1,055.8360	$1,055.84	$1,055.80	$1,055.70