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	$102.35	7.104%	$109.6209	$109.62	$109.60	$109.60
Purchase #2	$104.93	7.113%	$112.3937	$112.39	$112.40	$112.40
Purchase #3	$178.51	8.191%	$193.1318	$193.13	$193.15	$193.10
Purchase #4	$6.64	7.735%	$7.1536	$7.15	$7.15	$7.20
Purchase #5	$82.25	10.192%	$90.6329	$90.63	$90.65	$90.60
Purchase #6	$234.81	11.841%	$262.6139	$262.61	$262.60	$262.60
Purchase #7	$15.27	8.169%	$16.5174	$16.52	$16.50	$16.50
7 purchase totals =	$724.76		$792.0642	$792.05	$792.05	$792.00