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	$107.60	12.719%	$121.2856	$121.29	$121.30	$121.30
Purchase #2	$120.49	5.808%	$127.4881	$127.49	$127.50	$127.50
Purchase #3	$10.71	12.348%	$12.0325	$12.03	$12.05	$12.00
Purchase #4	$39.30	10.405%	$43.3892	$43.39	$43.40	$43.40
Purchase #5	$100.53	12.834%	$113.432	$113.43	$113.45	$113.40
Purchase #6	$157.45	5.766%	$166.5286	$166.53	$166.55	$166.50
Purchase #7	$83.47	3.191%	$86.1335	$86.13	$86.15	$86.10
7 purchase totals =	$619.55		$670.2895	$670.29	$670.40	$670.20