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	$55.31	7.739%	$59.5904	$59.59	$59.60	$59.60
Purchase #2	$167.55	3.619%	$173.6136	$173.61	$173.60	$173.60
Purchase #3	$160.84	6.342%	$171.0405	$171.04	$171.05	$171.00
Purchase #4	$235.51	13.283%	$266.7928	$266.79	$266.80	$266.80
Purchase #5	$42.43	9.631%	$46.5164	$46.52	$46.50	$46.50
Purchase #6	$103.97	10.722%	$115.1177	$115.12	$115.10	$115.10
Purchase #7	$119.40	10.275%	$131.6684	$131.67	$131.65	$131.70
7 purchase totals =	$885.01		$964.3398	$964.34	$964.30	$964.30