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	$78.84	13.332%	$89.3509	$89.35	$89.35	$89.40
Purchase #2	$100.70	6.410%	$107.1549	$107.15	$107.15	$107.20
Purchase #3	$114.35	10.738%	$126.6289	$126.63	$126.65	$126.60
Purchase #4	$116.64	6.807%	$124.5797	$124.58	$124.60	$124.60
Purchase #5	$79.83	9.569%	$87.4689	$87.47	$87.45	$87.50
Purchase #6	$39.78	6.349%	$42.3056	$42.31	$42.30	$42.30
Purchase #7	$43.30	12.631%	$48.7692	$48.77	$48.75	$48.80
7 purchase totals =	$573.44		$626.2581	$626.26	$626.25	$626.40