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	$49.52	12.682%	$55.8001	$55.80	$55.80	$55.80
Purchase #2	$122.83	4.366%	$128.1928	$128.19	$128.20	$128.20
Purchase #3	$14.51	13.172%	$16.4213	$16.42	$16.40	$16.40
Purchase #4	$109.77	12.835%	$123.859	$123.86	$123.85	$123.90
Purchase #5	$98.64	12.729%	$111.1959	$111.20	$111.20	$111.20
Purchase #6	$113.50	12.773%	$127.9974	$128.00	$128.00	$128.00
Purchase #7	$138.30	4.433%	$144.4308	$144.43	$144.45	$144.40
7 purchase totals =	$647.07		$707.8973	$707.90	$707.90	$707.90