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	$16.83	12.395%	$18.9161	$18.92	$18.90	$18.90
Purchase #2	$158.90	13.545%	$180.423	$180.42	$180.40	$180.40
Purchase #3	$34.91	13.334%	$39.5649	$39.56	$39.55	$39.60
Purchase #4	$188.80	5.678%	$199.5201	$199.52	$199.50	$199.50
Purchase #5	$186.97	13.678%	$212.5438	$212.54	$212.55	$212.50
Purchase #6	$100.48	3.579%	$104.0762	$104.08	$104.10	$104.10
Purchase #7	$51.90	5.793%	$54.9066	$54.91	$54.90	$54.90
7 purchase totals =	$738.79		$809.9507	$809.95	$809.90	$809.90