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	$71.52	9.738%	$78.4846	$78.48	$78.50	$78.50
Purchase #2	$26.83	12.291%	$30.1277	$30.13	$30.15	$30.10
Purchase #3	$212.85	5.215%	$223.9501	$223.95	$223.95	$224.00
Purchase #4	$231.92	10.874%	$257.139	$257.14	$257.15	$257.10
Purchase #5	$237.58	10.310%	$262.0745	$262.07	$262.05	$262.10
Purchase #6	$204.60	9.259%	$223.5439	$223.54	$223.55	$223.50
Purchase #7	$17.32	12.713%	$19.5219	$19.52	$19.50	$19.50
7 purchase totals =	$1,002.62		$1,094.8417	$1,094.83	$1,094.85	$1,094.80