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	$111.96	13.503%	$127.078	$127.08	$127.10	$127.10
Purchase #2	$66.68	6.389%	$70.9402	$70.94	$70.95	$70.90
Purchase #3	$247.84	4.804%	$259.7462	$259.75	$259.75	$259.70
Purchase #4	$20.29	3.705%	$21.0417	$21.04	$21.05	$21.00
Purchase #5	$219.49	13.603%	$249.3472	$249.35	$249.35	$249.30
Purchase #6	$83.92	7.720%	$90.3986	$90.40	$90.40	$90.40
Purchase #7	$145.70	5.212%	$153.2939	$153.29	$153.30	$153.30
7 purchase totals =	$895.88		$971.8458	$971.85	$971.90	$971.70