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	$167.37	11.221%	$186.1506	$186.15	$186.15	$186.20
Purchase #2	$43.77	13.303%	$49.5927	$49.59	$49.60	$49.60
Purchase #3	$19.46	10.685%	$21.5393	$21.54	$21.55	$21.50
Purchase #4	$11.74	9.460%	$12.8506	$12.85	$12.85	$12.90
Purchase #5	$115.40	3.239%	$119.1378	$119.14	$119.15	$119.10
Purchase #6	$64.42	9.161%	$70.3215	$70.32	$70.30	$70.30
Purchase #7	$158.78	7.607%	$170.8584	$170.86	$170.85	$170.90
7 purchase totals =	$580.94		$630.4509	$630.45	$630.45	$630.50