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	$43.56	13.476%	$49.4301	$49.43	$49.45	$49.40
Purchase #2	$137.67	5.805%	$145.6617	$145.66	$145.65	$145.70
Purchase #3	$230.86	6.196%	$245.1641	$245.16	$245.15	$245.20
Purchase #4	$66.57	8.364%	$72.1379	$72.14	$72.15	$72.10
Purchase #5	$163.74	13.397%	$185.6762	$185.68	$185.70	$185.70
Purchase #6	$10.43	3.443%	$10.7891	$10.79	$10.80	$10.80
Purchase #7	$71.39	9.452%	$78.1378	$78.14	$78.15	$78.10
7 purchase totals =	$724.22		$786.9969	$787.00	$787.05	$787.00