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	$111.74	6.374%	$118.8623	$118.86	$118.85	$118.90
Purchase #2	$165.80	13.420%	$188.0504	$188.05	$188.05	$188.10
Purchase #3	$124.81	11.871%	$139.6262	$139.63	$139.65	$139.60
Purchase #4	$50.42	8.245%	$54.5771	$54.58	$54.60	$54.60
Purchase #5	$15.98	6.487%	$17.0166	$17.02	$17.00	$17.00
Purchase #6	$6.79	9.637%	$7.4444	$7.44	$7.45	$7.40
Purchase #7	$105.57	5.285%	$111.1494	$111.15	$111.15	$111.10
7 purchase totals =	$581.11		$636.7264	$636.73	$636.75	$636.70