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	$81.54	11.345%	$90.7907	$90.79	$90.80	$90.80
Purchase #2	$38.42	4.853%	$40.2845	$40.28	$40.30	$40.30
Purchase #3	$110.60	5.730%	$116.9374	$116.94	$116.95	$116.90
Purchase #4	$37.93	11.473%	$42.2817	$42.28	$42.30	$42.30
Purchase #5	$28.98	8.286%	$31.3813	$31.38	$31.40	$31.40
Purchase #6	$136.42	12.497%	$153.4684	$153.47	$153.45	$153.50
Purchase #7	$33.85	12.433%	$38.0586	$38.06	$38.05	$38.10
7 purchase totals =	$467.74		$513.2026	$513.20	$513.25	$513.30