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	$6.78	7.557%	$7.2924	$7.29	$7.30	$7.30
Purchase #2	$51.81	3.786%	$53.7715	$53.77	$53.75	$53.80
Purchase #3	$183.54	13.393%	$208.1215	$208.12	$208.10	$208.10
Purchase #4	$158.37	13.528%	$179.7943	$179.79	$179.80	$179.80
Purchase #5	$59.37	7.680%	$63.9296	$63.93	$63.95	$63.90
Purchase #6	$169.54	9.351%	$185.3937	$185.39	$185.40	$185.40
Purchase #7	$166.79	3.628%	$172.8411	$172.84	$172.85	$172.80
7 purchase totals =	$796.20		$871.1441	$871.13	$871.15	$871.10