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	$49.31	9.853%	$54.1685	$54.17	$54.15	$54.20
Purchase #2	$249.25	12.269%	$279.8305	$279.83	$279.85	$279.80
Purchase #3	$7.97	6.307%	$8.4727	$8.47	$8.45	$8.50
Purchase #4	$28.47	10.848%	$31.5584	$31.56	$31.55	$31.60
Purchase #5	$147.48	3.466%	$152.5917	$152.59	$152.60	$152.60
Purchase #6	$102.80	8.400%	$111.4352	$111.44	$111.45	$111.40
Purchase #7	$18.86	12.837%	$21.2811	$21.28	$21.30	$21.30
7 purchase totals =	$604.14		$659.3381	$659.34	$659.35	$659.40