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	$164.93	12.864%	$186.1466	$186.15	$186.15	$186.10
Purchase #2	$184.45	11.376%	$205.433	$205.43	$205.45	$205.40
Purchase #3	$245.49	13.615%	$278.9135	$278.91	$278.90	$278.90
Purchase #4	$55.58	12.104%	$62.3074	$62.31	$62.30	$62.30
Purchase #5	$46.38	3.771%	$48.129	$48.13	$48.15	$48.10
Purchase #6	$64.50	9.255%	$70.4695	$70.47	$70.45	$70.50
Purchase #7	$157.76	5.374%	$166.238	$166.24	$166.25	$166.20
7 purchase totals =	$919.09		$1,017.6370	$1,017.64	$1,017.65	$1,017.50