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	$17.55	6.441%	$18.6804	$18.68	$18.70	$18.70
Purchase #2	$165.38	8.155%	$178.8667	$178.87	$178.85	$178.90
Purchase #3	$35.69	5.238%	$37.5594	$37.56	$37.55	$37.60
Purchase #4	$41.86	12.566%	$47.1201	$47.12	$47.10	$47.10
Purchase #5	$37.85	13.145%	$42.8254	$42.83	$42.85	$42.80
Purchase #6	$112.82	9.163%	$123.1577	$123.16	$123.15	$123.20
Purchase #7	$127.55	13.230%	$144.4249	$144.42	$144.40	$144.40
7 purchase totals =	$538.70		$592.6346	$592.64	$592.60	$592.70