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	$149.29	7.440%	$160.3972	$160.40	$160.40	$160.40
Purchase #2	$243.46	5.223%	$256.1759	$256.18	$256.20	$256.20
Purchase #3	$131.42	7.634%	$141.4526	$141.45	$141.45	$141.50
Purchase #4	$184.25	11.349%	$205.1605	$205.16	$205.15	$205.20
Purchase #5	$194.77	10.429%	$215.0826	$215.08	$215.10	$215.10
Purchase #6	$226.81	12.435%	$255.0138	$255.01	$255.00	$255.00
Purchase #7	$153.31	4.469%	$160.1614	$160.16	$160.15	$160.20
7 purchase totals =	$1,283.31		$1,393.4440	$1,393.44	$1,393.45	$1,393.60