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	$34.43	12.861%	$38.858	$38.86	$38.85	$38.90
Purchase #2	$89.84	9.653%	$98.5123	$98.51	$98.50	$98.50
Purchase #3	$50.63	9.808%	$55.5958	$55.60	$55.60	$55.60
Purchase #4	$62.60	12.503%	$70.4269	$70.43	$70.45	$70.40
Purchase #5	$114.42	11.198%	$127.2328	$127.23	$127.25	$127.20
Purchase #6	$204.68	12.775%	$230.8279	$230.83	$230.85	$230.80
Purchase #7	$29.45	10.310%	$32.4863	$32.49	$32.50	$32.50
7 purchase totals =	$586.05		$653.9400	$653.95	$654.00	$653.90