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	$100.75	3.825%	$104.6037	$104.60	$104.60	$104.60
Purchase #2	$207.98	4.852%	$218.0712	$218.07	$218.05	$218.10
Purchase #3	$23.46	7.433%	$25.2038	$25.20	$25.20	$25.20
Purchase #4	$28.65	12.292%	$32.1717	$32.17	$32.15	$32.20
Purchase #5	$53.67	11.531%	$59.8587	$59.86	$59.85	$59.90
Purchase #6	$72.45	13.152%	$81.9786	$81.98	$82.00	$82.00
Purchase #7	$111.78	7.186%	$119.8125	$119.81	$119.80	$119.80
7 purchase totals =	$598.74		$641.7002	$641.69	$641.65	$641.80