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	$90.97	10.243%	$100.2881	$100.29	$100.30	$100.30
Purchase #2	$127.78	9.529%	$139.9562	$139.96	$139.95	$140.00
Purchase #3	$138.68	13.130%	$156.8887	$156.89	$156.90	$156.90
Purchase #4	$60.42	12.407%	$67.9163	$67.92	$67.90	$67.90
Purchase #5	$56.34	3.162%	$58.1215	$58.12	$58.10	$58.10
Purchase #6	$245.53	10.855%	$272.1823	$272.18	$272.20	$272.20
Purchase #7	$145.30	7.139%	$155.673	$155.67	$155.65	$155.70
7 purchase totals =	$865.02		$951.0261	$951.03	$951.00	$951.10