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	$98.41	3.132%	$101.4922	$101.49	$101.50	$101.50
Purchase #2	$29.32	7.684%	$31.5729	$31.57	$31.55	$31.60
Purchase #3	$95.55	8.308%	$103.4883	$103.49	$103.50	$103.50
Purchase #4	$57.54	13.510%	$65.3137	$65.31	$65.30	$65.30
Purchase #5	$226.42	6.810%	$241.8392	$241.84	$241.85	$241.80
Purchase #6	$84.32	7.717%	$90.827	$90.83	$90.85	$90.80
Purchase #7	$165.30	3.216%	$170.616	$170.62	$170.60	$170.60
7 purchase totals =	$756.86		$805.1493	$805.15	$805.15	$805.10