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	$66.43	10.341%	$73.2995	$73.30	$73.30	$73.30
Purchase #2	$80.89	3.255%	$83.523	$83.52	$83.50	$83.50
Purchase #3	$94.95	7.200%	$101.7864	$101.79	$101.80	$101.80
Purchase #4	$72.80	10.341%	$80.3282	$80.33	$80.35	$80.30
Purchase #5	$24.89	11.539%	$27.7621	$27.76	$27.75	$27.80
Purchase #6	$237.82	13.274%	$269.3882	$269.39	$269.40	$269.40
Purchase #7	$51.54	5.685%	$54.47	$54.47	$54.45	$54.50
7 purchase totals =	$629.32		$690.5574	$690.56	$690.55	$690.60