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	$45.39	13.638%	$51.5803	$51.58	$51.60	$51.60
Purchase #2	$113.47	3.486%	$117.4256	$117.43	$117.45	$117.40
Purchase #3	$126.48	12.639%	$142.4658	$142.47	$142.45	$142.50
Purchase #4	$152.68	13.526%	$173.3315	$173.33	$173.35	$173.30
Purchase #5	$110.82	8.666%	$120.4237	$120.42	$120.40	$120.40
Purchase #6	$131.33	10.648%	$145.314	$145.31	$145.30	$145.30
Purchase #7	$86.86	3.242%	$89.676	$89.68	$89.70	$89.70
7 purchase totals =	$767.03		$840.2169	$840.22	$840.25	$840.20