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	$38.82	9.627%	$42.5572	$42.56	$42.55	$42.60
Purchase #2	$17.98	11.863%	$20.113	$20.11	$20.10	$20.10
Purchase #3	$66.52	8.342%	$72.0691	$72.07	$72.05	$72.10
Purchase #4	$78.31	8.534%	$84.993	$84.99	$85.00	$85.00
Purchase #5	$127.71	8.511%	$138.5794	$138.58	$138.60	$138.60
Purchase #6	$164.73	6.143%	$174.8494	$174.85	$174.85	$174.80
Purchase #7	$86.97	5.363%	$91.6342	$91.63	$91.65	$91.60
7 purchase totals =	$581.04		$624.7953	$624.79	$624.80	$624.80