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	$97.70	3.192%	$100.8186	$100.82	$100.80	$100.80
Purchase #2	$123.25	6.379%	$131.1121	$131.11	$131.10	$131.10
Purchase #3	$24.49	11.541%	$27.3164	$27.32	$27.30	$27.30
Purchase #4	$216.58	6.266%	$230.1509	$230.15	$230.15	$230.20
Purchase #5	$132.39	5.346%	$139.4676	$139.47	$139.45	$139.50
Purchase #6	$247.29	13.656%	$281.0599	$281.06	$281.05	$281.10
Purchase #7	$48.32	4.764%	$50.622	$50.62	$50.60	$50.60
7 purchase totals =	$890.02		$960.5475	$960.55	$960.45	$960.60