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	$12.50	3.667%	$12.9584	$12.96	$12.95	$13.00
Purchase #2	$219.60	8.687%	$238.6767	$238.68	$238.70	$238.70
Purchase #3	$210.36	10.847%	$233.1777	$233.18	$233.20	$233.20
Purchase #4	$101.96	3.397%	$105.4236	$105.42	$105.40	$105.40
Purchase #5	$213.53	4.424%	$222.9766	$222.98	$223.00	$223.00
Purchase #6	$54.97	6.455%	$58.5183	$58.52	$58.50	$58.50
Purchase #7	$200.49	13.863%	$228.2839	$228.28	$228.30	$228.30
7 purchase totals =	$1,013.41		$1,100.0152	$1,100.02	$1,100.05	$1,100.10