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	$246.92	11.530%	$275.3899	$275.39	$275.40	$275.40
Purchase #2	$161.32	10.653%	$178.5054	$178.51	$178.50	$178.50
Purchase #3	$175.42	10.112%	$193.1585	$193.16	$193.15	$193.20
Purchase #4	$238.64	8.602%	$259.1678	$259.17	$259.15	$259.20
Purchase #5	$246.50	8.632%	$267.7779	$267.78	$267.80	$267.80
Purchase #6	$63.42	6.387%	$67.4706	$67.47	$67.45	$67.50
Purchase #7	$150.50	9.358%	$164.5838	$164.58	$164.60	$164.60
7 purchase totals =	$1,282.72		$1,406.0539	$1,406.06	$1,406.05	$1,406.20