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	$102.44	8.774%	$111.4281	$111.43	$111.45	$111.40
Purchase #2	$136.77	11.649%	$152.7023	$152.70	$152.70	$152.70
Purchase #3	$8.43	4.654%	$8.8223	$8.82	$8.80	$8.80
Purchase #4	$127.33	10.298%	$140.4424	$140.44	$140.45	$140.40
Purchase #5	$91.42	4.335%	$95.3831	$95.38	$95.40	$95.40
Purchase #6	$74.44	10.145%	$81.9919	$81.99	$82.00	$82.00
Purchase #7	$45.52	12.213%	$51.0794	$51.08	$51.10	$51.10
7 purchase totals =	$586.35		$641.8495	$641.84	$641.90	$641.80