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	$46.48	10.418%	$51.3223	$51.32	$51.30	$51.30
Purchase #2	$150.52	10.831%	$166.8228	$166.82	$166.80	$166.80
Purchase #3	$115.98	9.677%	$127.2034	$127.20	$127.20	$127.20
Purchase #4	$227.35	8.836%	$247.4386	$247.44	$247.45	$247.40
Purchase #5	$46.42	12.872%	$52.3952	$52.40	$52.40	$52.40
Purchase #6	$208.82	4.759%	$218.7577	$218.76	$218.75	$218.80
Purchase #7	$39.85	13.246%	$45.1285	$45.13	$45.15	$45.10
7 purchase totals =	$835.42		$909.0685	$909.07	$909.05	$909.00