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	$139.72	8.338%	$151.3699	$151.37	$151.35	$151.40
Purchase #2	$97.42	8.379%	$105.5828	$105.58	$105.60	$105.60
Purchase #3	$64.40	8.689%	$69.9957	$70.00	$70.00	$70.00
Purchase #4	$115.37	10.692%	$127.7054	$127.71	$127.70	$127.70
Purchase #5	$141.55	6.187%	$150.3077	$150.31	$150.30	$150.30
Purchase #6	$65.39	11.271%	$72.7601	$72.76	$72.75	$72.80
Purchase #7	$93.69	7.510%	$100.7261	$100.73	$100.75	$100.70
7 purchase totals =	$717.54		$778.4477	$778.46	$778.45	$778.50