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	$230.28	12.859%	$259.8917	$259.89	$259.90	$259.90
Purchase #2	$243.46	5.729%	$257.4078	$257.41	$257.40	$257.40
Purchase #3	$14.89	4.151%	$15.5081	$15.51	$15.50	$15.50
Purchase #4	$53.50	7.495%	$57.5098	$57.51	$57.50	$57.50
Purchase #5	$8.56	4.161%	$8.9162	$8.92	$8.90	$8.90
Purchase #6	$136.32	8.630%	$148.0844	$148.08	$148.10	$148.10
Purchase #7	$152.46	3.792%	$158.2413	$158.24	$158.25	$158.20
7 purchase totals =	$839.47		$905.5593	$905.56	$905.55	$905.50