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	$126.72	7.409%	$136.1087	$136.11	$136.10	$136.10
Purchase #2	$50.46	5.784%	$53.3786	$53.38	$53.40	$53.40
Purchase #3	$90.54	10.793%	$100.312	$100.31	$100.30	$100.30
Purchase #4	$55.70	12.493%	$62.6586	$62.66	$62.65	$62.70
Purchase #5	$233.45	10.548%	$258.0743	$258.07	$258.05	$258.10
Purchase #6	$103.52	3.425%	$107.0656	$107.07	$107.05	$107.10
Purchase #7	$78.80	5.429%	$83.0781	$83.08	$83.10	$83.10
7 purchase totals =	$739.19		$800.6759	$800.68	$800.65	$800.80