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	$48.26	5.390%	$50.8612	$50.86	$50.85	$50.90
Purchase #2	$41.92	13.722%	$47.6723	$47.67	$47.65	$47.70
Purchase #3	$77.67	8.641%	$84.3815	$84.38	$84.40	$84.40
Purchase #4	$81.45	10.699%	$90.1643	$90.16	$90.15	$90.20
Purchase #5	$179.54	4.560%	$187.727	$187.73	$187.75	$187.70
Purchase #6	$77.34	6.824%	$82.6177	$82.62	$82.60	$82.60
Purchase #7	$11.93	7.517%	$12.8268	$12.83	$12.85	$12.80
7 purchase totals =	$518.11		$556.2508	$556.25	$556.25	$556.30