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	$108.92	6.586%	$116.0935	$116.09	$116.10	$116.10
Purchase #2	$152.98	3.681%	$158.6112	$158.61	$158.60	$158.60
Purchase #3	$73.62	10.253%	$81.1683	$81.17	$81.15	$81.20
Purchase #4	$146.62	13.780%	$166.8242	$166.82	$166.80	$166.80
Purchase #5	$63.58	4.426%	$66.3941	$66.39	$66.40	$66.40
Purchase #6	$166.68	4.658%	$174.444	$174.44	$174.45	$174.40
Purchase #7	$185.90	5.445%	$196.0223	$196.02	$196.00	$196.00
7 purchase totals =	$898.30		$959.5576	$959.54	$959.50	$959.50