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	$34.31	10.394%	$37.8762	$37.88	$37.90	$37.90
Purchase #2	$49.54	10.204%	$54.5951	$54.60	$54.60	$54.60
Purchase #3	$109.97	7.789%	$118.5356	$118.54	$118.55	$118.50
Purchase #4	$166.52	9.656%	$182.5992	$182.60	$182.60	$182.60
Purchase #5	$136.74	7.830%	$147.4467	$147.45	$147.45	$147.40
Purchase #6	$199.43	8.149%	$215.6816	$215.68	$215.70	$215.70
Purchase #7	$211.88	4.789%	$222.0269	$222.03	$222.05	$222.00
7 purchase totals =	$908.39		$978.7613	$978.78	$978.85	$978.70