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	$107.52	10.533%	$118.8451	$118.85	$118.85	$118.80
Purchase #2	$95.73	12.187%	$107.3966	$107.40	$107.40	$107.40
Purchase #3	$123.30	11.834%	$137.8913	$137.89	$137.90	$137.90
Purchase #4	$127.47	11.660%	$142.333	$142.33	$142.35	$142.30
Purchase #5	$66.71	11.579%	$74.4344	$74.43	$74.45	$74.40
Purchase #6	$80.51	3.191%	$83.0791	$83.08	$83.10	$83.10
Purchase #7	$152.99	8.858%	$166.5419	$166.54	$166.55	$166.50
7 purchase totals =	$754.23		$830.5214	$830.52	$830.60	$830.40