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	$231.57	12.192%	$259.803	$259.80	$259.80	$259.80
Purchase #2	$233.84	9.710%	$256.5459	$256.55	$256.55	$256.50
Purchase #3	$233.41	12.366%	$262.2735	$262.27	$262.25	$262.30
Purchase #4	$78.92	13.403%	$89.4976	$89.50	$89.50	$89.50
Purchase #5	$139.82	9.720%	$153.4105	$153.41	$153.40	$153.40
Purchase #6	$177.92	5.683%	$188.0312	$188.03	$188.05	$188.00
Purchase #7	$218.31	3.824%	$226.6582	$226.66	$226.65	$226.70
7 purchase totals =	$1,313.79		$1,436.2199	$1,436.22	$1,436.20	$1,436.20