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	$224.99	13.388%	$255.1117	$255.11	$255.10	$255.10
Purchase #2	$153.96	6.861%	$164.5232	$164.52	$164.50	$164.50
Purchase #3	$121.77	10.508%	$134.5656	$134.57	$134.55	$134.60
Purchase #4	$43.28	5.310%	$45.5782	$45.58	$45.60	$45.60
Purchase #5	$48.91	3.485%	$50.6145	$50.61	$50.60	$50.60
Purchase #6	$74.50	10.436%	$82.2748	$82.27	$82.25	$82.30
Purchase #7	$219.72	9.789%	$241.2284	$241.23	$241.25	$241.20
7 purchase totals =	$887.13		$973.8964	$973.89	$973.85	$973.90