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	$234.82	12.231%	$263.5408	$263.54	$263.55	$263.50
Purchase #2	$205.54	6.380%	$218.6535	$218.65	$218.65	$218.70
Purchase #3	$19.82	3.424%	$20.4986	$20.50	$20.50	$20.50
Purchase #4	$153.38	13.153%	$173.5541	$173.55	$173.55	$173.60
Purchase #5	$47.45	4.615%	$49.6398	$49.64	$49.65	$49.60
Purchase #6	$11.38	9.151%	$12.4214	$12.42	$12.40	$12.40
Purchase #7	$142.78	9.606%	$156.4954	$156.50	$156.50	$156.50
7 purchase totals =	$815.17		$894.8036	$894.80	$894.80	$894.80