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	$37.51	4.222%	$39.0937	$39.09	$39.10	$39.10
Purchase #2	$155.89	4.345%	$162.6634	$162.66	$162.65	$162.70
Purchase #3	$19.98	8.566%	$21.6915	$21.69	$21.70	$21.70
Purchase #4	$46.95	12.746%	$52.9342	$52.93	$52.95	$52.90
Purchase #5	$200.34	11.721%	$223.8219	$223.82	$223.80	$223.80
Purchase #6	$38.63	11.463%	$43.0582	$43.06	$43.05	$43.10
Purchase #7	$138.44	10.710%	$153.2669	$153.27	$153.25	$153.30
7 purchase totals =	$637.74		$696.5298	$696.52	$696.50	$696.60