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	$81.29	11.325%	$90.4961	$90.50	$90.50	$90.50
Purchase #2	$242.65	12.565%	$273.139	$273.14	$273.15	$273.10
Purchase #3	$134.60	3.852%	$139.7848	$139.78	$139.80	$139.80
Purchase #4	$130.26	12.508%	$146.5529	$146.55	$146.55	$146.60
Purchase #5	$104.84	11.204%	$116.5863	$116.59	$116.60	$116.60
Purchase #6	$37.42	4.170%	$38.9804	$38.98	$39.00	$39.00
Purchase #7	$5.84	10.490%	$6.4526	$6.45	$6.45	$6.50
7 purchase totals =	$736.90		$811.9921	$811.99	$812.05	$812.10