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	$161.72	10.239%	$178.2785	$178.28	$178.30	$178.30
Purchase #2	$91.84	12.798%	$103.5937	$103.59	$103.60	$103.60
Purchase #3	$242.97	8.406%	$263.3941	$263.39	$263.40	$263.40
Purchase #4	$123.45	6.366%	$131.3088	$131.31	$131.30	$131.30
Purchase #5	$99.45	13.370%	$112.7465	$112.75	$112.75	$112.70
Purchase #6	$37.27	10.858%	$41.3168	$41.32	$41.30	$41.30
Purchase #7	$129.53	7.379%	$139.088	$139.09	$139.10	$139.10
7 purchase totals =	$886.23		$969.7264	$969.73	$969.75	$969.70