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	$13.83	12.242%	$15.5231	$15.52	$15.50	$15.50
Purchase #2	$167.31	7.438%	$179.7545	$179.75	$179.75	$179.80
Purchase #3	$239.65	13.317%	$271.5642	$271.56	$271.55	$271.60
Purchase #4	$102.70	5.481%	$108.329	$108.33	$108.35	$108.30
Purchase #5	$210.99	10.696%	$233.5575	$233.56	$233.55	$233.60
Purchase #6	$151.45	10.358%	$167.1372	$167.14	$167.15	$167.10
Purchase #7	$61.85	5.301%	$65.1287	$65.13	$65.15	$65.10
7 purchase totals =	$947.78		$1,040.9942	$1,040.99	$1,041.00	$1,041.00