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	$226.52	13.693%	$257.5374	$257.54	$257.55	$257.50
Purchase #2	$242.94	12.243%	$272.6831	$272.68	$272.70	$272.70
Purchase #3	$147.37	4.221%	$153.5905	$153.59	$153.60	$153.60
Purchase #4	$248.30	10.487%	$274.3392	$274.34	$274.35	$274.30
Purchase #5	$173.46	13.526%	$196.9222	$196.92	$196.90	$196.90
Purchase #6	$167.83	6.129%	$178.1163	$178.12	$178.10	$178.10
Purchase #7	$175.80	7.231%	$188.5121	$188.51	$188.50	$188.50
7 purchase totals =	$1,382.22		$1,521.7008	$1,521.70	$1,521.70	$1,521.60