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	$72.92	6.323%	$77.5307	$77.53	$77.55	$77.50
Purchase #2	$97.63	13.832%	$111.1342	$111.13	$111.15	$111.10
Purchase #3	$248.95	9.813%	$273.3795	$273.38	$273.40	$273.40
Purchase #4	$98.71	8.757%	$107.354	$107.35	$107.35	$107.40
Purchase #5	$72.76	10.722%	$80.5613	$80.56	$80.55	$80.60
Purchase #6	$115.62	10.269%	$127.493	$127.49	$127.50	$127.50
Purchase #7	$103.80	9.318%	$113.4721	$113.47	$113.45	$113.50
7 purchase totals =	$810.39		$890.9248	$890.91	$890.95	$891.00