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	$234.43	11.512%	$261.4176	$261.42	$261.40	$261.40
Purchase #2	$77.87	9.277%	$85.094	$85.09	$85.10	$85.10
Purchase #3	$176.98	6.868%	$189.135	$189.14	$189.15	$189.10
Purchase #4	$119.90	6.242%	$127.3842	$127.38	$127.40	$127.40
Purchase #5	$11.61	5.832%	$12.2871	$12.29	$12.30	$12.30
Purchase #6	$113.72	10.193%	$125.3115	$125.31	$125.30	$125.30
Purchase #7	$52.96	3.105%	$54.6044	$54.60	$54.60	$54.60
7 purchase totals =	$787.47		$855.2338	$855.23	$855.25	$855.20