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	$136.45	13.531%	$154.913	$154.91	$154.90	$154.90
Purchase #2	$209.67	8.107%	$226.6679	$226.67	$226.65	$226.70
Purchase #3	$133.56	10.689%	$147.8362	$147.84	$147.85	$147.80
Purchase #4	$45.45	10.695%	$50.3109	$50.31	$50.30	$50.30
Purchase #5	$127.28	3.466%	$131.6915	$131.69	$131.70	$131.70
Purchase #6	$111.54	10.340%	$123.0732	$123.07	$123.05	$123.10
Purchase #7	$53.93	13.396%	$61.1545	$61.15	$61.15	$61.20
7 purchase totals =	$817.88		$895.6472	$895.64	$895.60	$895.70