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	$86.83	12.258%	$97.4736	$97.47	$97.45	$97.50
Purchase #2	$51.52	6.508%	$54.8729	$54.87	$54.85	$54.90
Purchase #3	$237.69	3.831%	$246.7959	$246.80	$246.80	$246.80
Purchase #4	$29.90	10.615%	$33.0739	$33.07	$33.05	$33.10
Purchase #5	$115.83	12.627%	$130.4559	$130.46	$130.45	$130.50
Purchase #6	$53.97	13.763%	$61.3979	$61.40	$61.40	$61.40
Purchase #7	$49.34	13.794%	$56.146	$56.15	$56.15	$56.10
7 purchase totals =	$625.08		$680.2161	$680.22	$680.15	$680.30