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	$152.27	9.335%	$166.4844	$166.48	$166.50	$166.50
Purchase #2	$234.87	13.800%	$267.2821	$267.28	$267.30	$267.30
Purchase #3	$37.70	3.866%	$39.1575	$39.16	$39.15	$39.20
Purchase #4	$6.59	4.391%	$6.8794	$6.88	$6.90	$6.90
Purchase #5	$94.30	12.177%	$105.7829	$105.78	$105.80	$105.80
Purchase #6	$120.42	13.783%	$137.0175	$137.02	$137.00	$137.00
Purchase #7	$68.43	13.451%	$77.6345	$77.63	$77.65	$77.60
7 purchase totals =	$714.58		$800.2383	$800.23	$800.30	$800.30