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	$70.75	10.740%	$78.3486	$78.35	$78.35	$78.30
Purchase #2	$11.76	6.770%	$12.5562	$12.56	$12.55	$12.60
Purchase #3	$199.25	4.198%	$207.6145	$207.61	$207.60	$207.60
Purchase #4	$19.83	9.806%	$21.7745	$21.77	$21.75	$21.80
Purchase #5	$96.62	13.151%	$109.3265	$109.33	$109.35	$109.30
Purchase #6	$106.65	6.168%	$113.2282	$113.23	$113.25	$113.20
Purchase #7	$24.40	13.268%	$27.6374	$27.64	$27.65	$27.60
7 purchase totals =	$529.26		$570.4859	$570.49	$570.50	$570.40