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	$90.37	11.372%	$100.6469	$100.65	$100.65	$100.60
Purchase #2	$66.31	10.794%	$73.4675	$73.47	$73.45	$73.50
Purchase #3	$180.94	12.746%	$204.0026	$204.00	$204.00	$204.00
Purchase #4	$110.78	11.167%	$123.1508	$123.15	$123.15	$123.20
Purchase #5	$58.96	10.340%	$65.0565	$65.06	$65.05	$65.10
Purchase #6	$12.75	4.277%	$13.2953	$13.30	$13.30	$13.30
Purchase #7	$123.93	5.467%	$130.7053	$130.71	$130.70	$130.70
7 purchase totals =	$644.04		$710.3249	$710.34	$710.30	$710.40