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	$176.83	6.820%	$188.8898	$188.89	$188.90	$188.90
Purchase #2	$49.82	9.105%	$54.3561	$54.36	$54.35	$54.40
Purchase #3	$107.76	7.792%	$116.1567	$116.16	$116.15	$116.20
Purchase #4	$146.93	3.392%	$151.9139	$151.91	$151.90	$151.90
Purchase #5	$181.57	5.398%	$191.3711	$191.37	$191.35	$191.40
Purchase #6	$9.60	7.679%	$10.3372	$10.34	$10.35	$10.30
Purchase #7	$146.84	9.245%	$160.4154	$160.42	$160.40	$160.40
7 purchase totals =	$819.35		$873.4402	$873.45	$873.40	$873.50