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	$39.91	9.328%	$43.6328	$43.63	$43.65	$43.60
Purchase #2	$167.79	12.433%	$188.6513	$188.65	$188.65	$188.70
Purchase #3	$107.88	3.233%	$111.3678	$111.37	$111.35	$111.40
Purchase #4	$151.60	5.196%	$159.4771	$159.48	$159.50	$159.50
Purchase #5	$91.82	12.346%	$103.1561	$103.16	$103.15	$103.20
Purchase #6	$80.73	9.262%	$88.2072	$88.21	$88.20	$88.20
Purchase #7	$162.33	10.154%	$178.813	$178.81	$178.80	$178.80
7 purchase totals =	$802.06		$873.3053	$873.31	$873.30	$873.40