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	$39.37	8.212%	$42.6031	$42.60	$42.60	$42.60
Purchase #2	$18.44	13.329%	$20.8979	$20.90	$20.90	$20.90
Purchase #3	$193.29	8.233%	$209.2036	$209.20	$209.20	$209.20
Purchase #4	$80.69	13.245%	$91.3774	$91.38	$91.40	$91.40
Purchase #5	$105.60	5.850%	$111.7776	$111.78	$111.80	$111.80
Purchase #6	$160.30	8.411%	$173.7828	$173.78	$173.80	$173.80
Purchase #7	$34.83	11.337%	$38.7787	$38.78	$38.80	$38.80
7 purchase totals =	$632.52		$688.4211	$688.42	$688.50	$688.50