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	$199.39	8.169%	$215.6782	$215.68	$215.70	$215.70
Purchase #2	$151.42	10.417%	$167.1934	$167.19	$167.20	$167.20
Purchase #3	$152.90	12.786%	$172.4498	$172.45	$172.45	$172.40
Purchase #4	$134.97	8.555%	$146.5167	$146.52	$146.50	$146.50
Purchase #5	$23.25	9.738%	$25.5141	$25.51	$25.50	$25.50
Purchase #6	$238.99	13.843%	$272.0734	$272.07	$272.05	$272.10
Purchase #7	$130.33	9.179%	$142.293	$142.29	$142.30	$142.30
7 purchase totals =	$1,031.25		$1,141.7186	$1,141.71	$1,141.70	$1,141.70