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	$115.95	4.539%	$121.213	$121.21	$121.20	$121.20
Purchase #2	$81.70	10.853%	$90.5669	$90.57	$90.55	$90.60
Purchase #3	$111.31	12.146%	$124.8297	$124.83	$124.85	$124.80
Purchase #4	$73.93	11.307%	$82.2893	$82.29	$82.30	$82.30
Purchase #5	$72.55	10.498%	$80.1663	$80.17	$80.15	$80.20
Purchase #6	$218.35	9.267%	$238.5845	$238.58	$238.60	$238.60
Purchase #7	$32.37	7.405%	$34.767	$34.77	$34.75	$34.80
7 purchase totals =	$706.16		$772.4167	$772.42	$772.40	$772.50