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	$142.91	11.667%	$159.5833	$159.58	$159.60	$159.60
Purchase #2	$60.27	11.274%	$67.0648	$67.06	$67.05	$67.10
Purchase #3	$224.56	3.189%	$231.7212	$231.72	$231.70	$231.70
Purchase #4	$77.35	3.498%	$80.0557	$80.06	$80.05	$80.10
Purchase #5	$56.51	9.216%	$61.718	$61.72	$61.70	$61.70
Purchase #6	$188.27	5.236%	$198.1278	$198.13	$198.15	$198.10
Purchase #7	$250.83	11.526%	$279.7407	$279.74	$279.75	$279.70
7 purchase totals =	$1,000.70		$1,078.0115	$1,078.01	$1,078.00	$1,078.00