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	$32.37	11.616%	$36.1301	$36.13	$36.15	$36.10
Purchase #2	$160.87	7.720%	$173.2892	$173.29	$173.30	$173.30
Purchase #3	$91.77	11.398%	$102.2299	$102.23	$102.25	$102.20
Purchase #4	$72.42	13.550%	$82.2329	$82.23	$82.25	$82.20
Purchase #5	$186.27	13.551%	$211.5114	$211.51	$211.50	$211.50
Purchase #6	$141.30	3.248%	$145.8894	$145.89	$145.90	$145.90
Purchase #7	$118.55	12.493%	$133.3605	$133.36	$133.35	$133.40
7 purchase totals =	$803.55		$884.6434	$884.64	$884.70	$884.60