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	$115.31	12.631%	$129.8748	$129.87	$129.85	$129.90
Purchase #2	$31.65	4.454%	$33.0597	$33.06	$33.05	$33.10
Purchase #3	$82.60	9.292%	$90.2752	$90.28	$90.30	$90.30
Purchase #4	$61.52	10.267%	$67.8363	$67.84	$67.85	$67.80
Purchase #5	$208.97	11.769%	$233.5637	$233.56	$233.55	$233.60
Purchase #6	$163.37	13.318%	$185.1276	$185.13	$185.15	$185.10
Purchase #7	$57.78	9.856%	$63.4748	$63.47	$63.45	$63.50
7 purchase totals =	$721.20		$803.2121	$803.21	$803.20	$803.30