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	$208.80	13.152%	$236.2614	$236.26	$236.25	$236.30
Purchase #2	$91.95	8.710%	$99.9588	$99.96	$99.95	$100.00
Purchase #3	$249.49	3.792%	$258.9507	$258.95	$258.95	$259.00
Purchase #4	$28.80	10.718%	$31.8868	$31.89	$31.90	$31.90
Purchase #5	$79.66	12.532%	$89.643	$89.64	$89.65	$89.60
Purchase #6	$56.92	8.612%	$61.822	$61.82	$61.80	$61.80
Purchase #7	$194.42	5.642%	$205.3892	$205.39	$205.40	$205.40
7 purchase totals =	$910.04		$983.9119	$983.91	$983.90	$984.00