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	$138.83	11.603%	$154.9384	$154.94	$154.95	$154.90
Purchase #2	$101.51	9.762%	$111.4194	$111.42	$111.40	$111.40
Purchase #3	$174.79	13.847%	$198.9932	$198.99	$199.00	$199.00
Purchase #4	$124.54	5.647%	$131.5728	$131.57	$131.55	$131.60
Purchase #5	$26.42	12.199%	$29.643	$29.64	$29.65	$29.60
Purchase #6	$73.93	6.372%	$78.6408	$78.64	$78.65	$78.60
Purchase #7	$188.29	9.152%	$205.5223	$205.52	$205.50	$205.50
7 purchase totals =	$828.31		$910.7299	$910.72	$910.70	$910.60