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	$225.28	12.124%	$252.5929	$252.59	$252.60	$252.60
Purchase #2	$21.71	11.604%	$24.2292	$24.23	$24.25	$24.20
Purchase #3	$104.77	10.174%	$115.4293	$115.43	$115.45	$115.40
Purchase #4	$89.34	11.601%	$99.7043	$99.70	$99.70	$99.70
Purchase #5	$241.37	5.798%	$255.3646	$255.36	$255.35	$255.40
Purchase #6	$90.83	12.231%	$101.9394	$101.94	$101.95	$101.90
Purchase #7	$202.67	10.109%	$223.1579	$223.16	$223.15	$223.20
7 purchase totals =	$975.97		$1,072.4176	$1,072.41	$1,072.45	$1,072.40