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	$113.91	3.783%	$118.2192	$118.22	$118.20	$118.20
Purchase #2	$164.33	5.540%	$173.4339	$173.43	$173.45	$173.40
Purchase #3	$126.69	10.694%	$140.2382	$140.24	$140.25	$140.20
Purchase #4	$101.73	13.335%	$115.2957	$115.30	$115.30	$115.30
Purchase #5	$83.73	6.713%	$89.3508	$89.35	$89.35	$89.40
Purchase #6	$13.64	6.258%	$14.4936	$14.49	$14.50	$14.50
Purchase #7	$12.84	3.642%	$13.3076	$13.31	$13.30	$13.30
7 purchase totals =	$616.87		$664.3390	$664.34	$664.35	$664.30